It is correct (belly). :-) I think I remember it being less painful when I was fatter? The 30G/8mm needles I'm using are smaller than your 27G/13mm needles in both dimensions; should be better, if anything. Again, it's not a big deal, but I feel it.

It’s mostly random and some people do feel it more than others.

It’s a rapidly absorbed peptide suspended in water, it could even be used with a transdermal patch, so it doesn’t matter that much where it gets in or how deep. Best to avoid painful areas though.