I'm a big fan of shooting with 1 inch on the thighs, I always shoot on the thighs. From what I read when shooting on the glutes you need 1,5 inch.If your bf is low enough you could do it with 1 inch on the glutes but why risk it? Shooting on the thighs works perfect for me.

Here is a very good video on how to shoot on the thigh How To Inject Testosterone - YouTube and it's the one I followed to shoot properly.