diff --git a/action.yaml b/action.yaml
index 77ad247..9bc8177 100644
--- a/action.yaml
+++ b/action.yaml
@@ -114,7 +114,7 @@ runs:
       env:
         MERGE_INSTANCE_BRANCH_HEAD_SHA:
           ${{ steps.prerequisites.outputs.merge_instance_branch_head_sha }}
-        PR_BRANCH_HEAD_SHA: ${{ steps.prerequisites.outputs.pr_branch_head_sha }}
+        PR_BRANCH_HEAD_SHA: ${{ steps.prerequisites.outputs.pr_branch_upload_head_sha }}
         VERBOSE: ${{ inputs.verbose }}
         WORKSPACE_PATH: ${{ steps.prerequisites.outputs.workspace_path }}
         BAZEL_PATH: ${{ inputs.bazel-path }}
@@ -132,7 +132,7 @@ runs:
         REPOSITORY: ${{ github.repository }}
         TARGET_BRANCH: ${{ steps.prerequisites.outputs.merge_instance_branch }}
         PR_NUMBER: ${{ github.event.pull_request.number }}
-        PR_SHA: ${{ steps.prerequisites.outputs.pr_branch_head_sha }}
+        PR_SHA: ${{ steps.prerequisites.outputs.pr_branch_upload_head_sha }}
         IMPACTED_TARGETS_FILE:
           ${{ steps.compute-impacted-targets-upload.outputs.impacted_targets_out }}
         IMPACTS_ALL_DETECTED: ${{ steps.prerequisites.outputs.impacts_all_detected }}
@@ -148,7 +148,7 @@ runs:
       env:
         # Use base sha instead of merge instance branch head sha for testing
         MERGE_INSTANCE_BRANCH_HEAD_SHA: ${{ steps.prerequisites.outputs.merge_base_sha }}
-        PR_BRANCH_HEAD_SHA: ${{ steps.prerequisites.outputs.pr_branch_head_sha }}
+        PR_BRANCH_HEAD_SHA: ${{ steps.prerequisites.outputs.pr_branch_testing_head_sha }}
         VERBOSE: ${{ inputs.verbose }}
         WORKSPACE_PATH: ${{ steps.prerequisites.outputs.workspace_path }}
         BAZEL_PATH: ${{ inputs.bazel-path }}
diff --git a/src/scripts/prerequisites.sh b/src/scripts/prerequisites.sh
index f87a8fc..25a67ad 100755
--- a/src/scripts/prerequisites.sh
+++ b/src/scripts/prerequisites.sh
@@ -59,13 +59,16 @@ else
 	merge_instance_branch_head_sha=$(git rev-parse "origin/${merge_instance_branch}")
 fi
 
-if ! pr_branch_head_sha=$(git rev-parse "${pr_branch}"); then
-	pr_branch_head_sha=$(git rev-parse "origin/${pr_branch}")
+if ! pr_branch_upload_head_sha=$(git rev-parse "${pr_branch}"); then
+	pr_branch_upload_head_sha=$(git rev-parse "origin/${pr_branch}")
 fi
+# Testing head SHA varies because we want to use HEAD rather than github.head_ref to accurately detect targets that are actually present to be queryable/testable
+pr_branch_testing_head_sha=$(git rev-parse "HEAD")
 
 # When testing, we use the merge-base rather than the HEAD of the target branch
-echo "Checking merge-base of PR Branch (${pr_branch_head_sha}) and merge branch (${merge_instance_branch_head_sha})"
+echo "Checking testing merge-base of PR Branch (${pr_branch_testing_head_sha}) and merge branch (${merge_instance_branch_head_sha})"
 merge_base_sha=$(git merge-base HEAD "${merge_instance_branch_head_sha}")
+echo "Got merge-base: ${merge_base_sha}"
 
 echo "Identified changes: " "${impacts_all_detected}"
 
@@ -86,10 +89,11 @@ fi
 # Outputs
 if [[ -v GITHUB_OUTPUT && -f ${GITHUB_OUTPUT} ]]; then
 	# trunk-ignore-begin(shellcheck/SC2129)
-	echo "merge_instance_branch=${merge_instance_branch}" >>"${GITHUB_OUTPUT}"
-	echo "merge_instance_branch_head_sha=${merge_instance_branch_head_sha}" >>"${GITHUB_OUTPUT}"
-	echo "merge_base_sha=${merge_base_sha}" >>"${GITHUB_OUTPUT}"
-	echo "pr_branch_head_sha=${pr_branch_head_sha}" >>"${GITHUB_OUTPUT}"
+	echo "merge_instance_branch=${merge_instance_branch}" >>"${GITHUB_OUTPUT}" # NOTE(TYLER): USED BY UPLOAD
+	echo "merge_instance_branch_head_sha=${merge_instance_branch_head_sha}" >>"${GITHUB_OUTPUT}" # NOTE(TYLER): USED BY BOTH COMPUTE
+	echo "merge_base_sha=${merge_base_sha}" >>"${GITHUB_OUTPUT}" # NOTE(TYLER): USED BY TESTING COMPUTE
+	echo "pr_branch_upload_head_sha=${pr_branch_upload_head_sha}" >>"${GITHUB_OUTPUT}" # NOTE(TYLER): USED BY BOTH COMPUTE AND UPLOAD -> upload and upload compute
+	echo "pr_branch_testing_head_sha=${pr_branch_testing_head_sha}" >>"${GITHUB_OUTPUT}" # NOTE(TYLER): USED BY TESTING COMPUTE
 	echo "impacts_all_detected=${impacts_all_detected}" >>"${GITHUB_OUTPUT}"
 	echo "workspace_path=${workspace_path}" >>"${GITHUB_OUTPUT}"
 	echo "requires_default_bazel_installation=${requires_default_bazel_installation}" >>"${GITHUB_OUTPUT}"
@@ -99,7 +103,8 @@ else
 	echo "::set-output name=merge_instance_branch::${merge_instance_branch}"
 	echo "::set-output name=merge_instance_branch_head_sha::${merge_instance_branch_head_sha}"
 	echo "::set-output name=merge_base_sha::${merge_base_sha}"
-	echo "::set-output name=pr_branch_head_sha::${pr_branch_head_sha}"
+	echo "::set-output name=pr_branch_upload_head_sha::${pr_branch_upload_head_sha}"
+	echo "::set-output name=pr_branch_testing_head_sha::${pr_branch_testing_head_sha}"
 	echo "::set-output name=impacts_all_detected::${impacts_all_detected}"
 	echo "::set-output name=workspace_path::${workspace_path}"
 	echo "::set-output name=requires_default_bazel_installation::${requires_default_bazel_installation}"
diff --git a/src/scripts/test_wrapper.sh b/src/scripts/test_wrapper.sh
index dc41999..3686789 100755
--- a/src/scripts/test_wrapper.sh
+++ b/src/scripts/test_wrapper.sh
@@ -81,7 +81,7 @@ touch "${GITHUB_OUTPUT}"
 
 # Use merge base sha instead of merge head sha to calculate the correct diff for testing.
 MERGE_INSTANCE_BRANCH_HEAD_SHA=$(awk -F "=" '$1=="merge_base_sha" {print $2}' "${GITHUB_OUTPUT}")
-PR_BRANCH_HEAD_SHA=$(awk -F "=" '$1=="pr_branch_head_sha" {print $2}' "${GITHUB_OUTPUT}")
+PR_BRANCH_HEAD_SHA=$(awk -F "=" '$1=="pr_branch_testing_head_sha" {print $2}' "${GITHUB_OUTPUT}")
 WORKSPACE_PATH=$(awk -F "=" '$1=="workspace_path" {print $2}' "${GITHUB_OUTPUT}")
 BAZEL_DIFF_CMD=$(awk -F "=" '$1=="bazel_diff_cmd" {print $2}' "${GITHUB_OUTPUT}")