^^^^ depends on how fat your ass is. 1.5 might be needed.. or for skinnier guys 1 inch is good enough. the angle you go in is important
this is why i don't like the glutes. if you have wide shoulders how can you even get there first off.. second off you using a mirror which can be tricky.
i like using the delts, pecs, and quads i can look at what i'm doing without a mirror