Welcome to the forum Wise!
There are a ton of threads about injecting. Most here do T via IM and not Subq. Some do it all Subq. It seems the preferred method of HCG is Subq for sure. As far as sitting or standing I can't believe it makes a difference. On the T injection the shoulders or the thigh seem to be preferred, I do shallow IM with a 1/2 27ga syringe. Some use 29ga. It's just a matter of preference really. Read all the FAQ's under Testosterone Basics regarding injections if you have not already.
I'm not familiar with TB500.