The length of the needle does not effect the pain in any way whatsoever the nerves aren't deep in the muscle. People who use short needles are just doing it out of fear... and it's misplaced. I prefer the shoot with a 25g needle unless the gear is too thick and then I'll use a 23g. 1.5" will work fine for you even if you are thin. My doctor used a 1" needle in my toddlers thigh so I'm pretty sure everyone here can get away with at least a 1" pin on any site and 1.5" on most. I use 1.5" on most of my sites. If I'm pinning my delt with a 1.5" I don't completely bury it but I'm sure if I did I still wouldn't hit the bone.