stat_coverage Y-axis limits or Y-max

[chrisgulvik]

How do I constrain the Y-axis for stat_coverage? Specifying ylim=(0,150) and ymax=150 doesn't work in aes() and prints "Error: subscript contains invalid names" but works without that part. Because coverage is so varied, I'd like to: (1) identify excess coverage sites, (2) constrain the coverage plot to something reasonable, say 150x, and (3) overlay excess coverage sites in red.

ggplot() + stat_coverage(short.bam, geom = 'line', col = 'blue', alpha = 0.2, aes(ymax=150)) + plotExcessCovSites