For me, it depends on the amount of oil I’m pinning. “In the muscle”, is in the muscle. Doesn’t matter how deep it is. What matters is how much oil I intend to stay in the muscle. If I’m too shallow and trying to pin a milliliter or more of oil, probably half is going to leak out of the muscle and essentially become sub q. Pinning .3 to .5ml it isn’t going to leak. Now if you are a bit over weight with higher body fat then of course shorter pins arent getting into the muscle at all. That’s why the 1" is often suggested. Just to ensure you are in the muscle.