Yes- size can play a factor in feeling movement (so I have read)- also the position of the baby and the uterus. On that note, the baby's personality also plays a factor- some are wigglers....and some are more chill.
Honestly- I wouldn't worry. At 16 weeks I would feel some movement, but very faint and inconsistent. It didn't really start to get really noticeable until 18 weeks, and consistent until 20 weeks.
I think part of why they say second (and more) time mothers feel movement earlier is because they can recognize the movement for what it is, and not pass it off as gas, digestion, etc. Haha, when I first started to feel movement, I just thought it was my digestive system doing it's thing! I know it's hard not to worry, but if the u/s says everything is fine, it's likely that the baby is perfectly fine in there and you just aren't feeling it quite yet. Hell, there are some days where I don't feel much, either because the baby isn't very active, or she has gotten into a position that isn't conducive to me feeling movement. I was told not to do kick counts and the like until about 28 weeks.....
Hope things continue to go well
