The problem is that the overflow = "compress" adjustment doesn't take into account the effective max bin count as calculated in dot_heap(). The right solution might be to optionally return the relevant info from find_dotplot_binwidth() so this check can be done.

An example showing the problem:

data.frame(x = dist_normal(0,1)) |> 
  ggplot(aes(xdist = x)) + 
  stat_dots(quantiles = 250, overflow = "compress", alpha = 0.5, binwidth = 0.5) + 
  geom_hline(yintercept = 0.9)

(alternative is to accept that overflow = "compress" is really only designed for when dots get very small, where it already works well).