library(ggplot2)
library(aplot)
df = data.frame(x=rnorm(100), y=rnorm(100))
p.scatter = ggplot(df, aes(x=x, y=y)) + geom_point()
p.xmargin = ggplot(df, aes(x=x)) + geom_histogram() 
p.ymargin = ggplot(df, aes(y=y)) + geom_histogram()

apx = p.scatter %>% insert_top(p.xmargin)
print(apx)  # works fine

# fix aspect ratio for scatter plot
apx[2,1] <- apx[2,1] + coord_fixed() 
print(apx) # x-axis is not aligned if canvas height:width < 2

# insert_right is also affected
apy = (p.scatter + coord_fixed()) %>%  insert_right(p.ymargin)
print(apy) # the y-axis is not aligned if canvas width:height < 2