Sorry, but I'm going to have to go ahead and call you out here mate.
Do you intend for an individual to stick a 1.5 inch 21 or 22 ga needle into oneself more than maybe once a week or so? Speaking purely from experience alone, I can tell you there is not much difference between your 21 or 22 and a 20 or even 18 used for drawing. Yea, they may look different, but that feeling of being crippled pretty much is all the same a day or so after you stick that puppy in your glute.
If you're going to inject 1.5 inches deep into yourself (unless you're a masochist) use at least a 25. I actually know of several guys who use 28 and that is injecting 1.25ml of test e at 250mg/ml. So don't even try and say that it won't flow through a needle that small. I personally have done this with a 28, but instead use a 25 simply because of the fact it doesn't stay in me near as long.
Like Bushy said, draw on some real world experience before you start trying to tell somebody what to do because of something you read in some book.