A pop-up question for bigger boards

Right, before I start, I don't mean to be mean, but I'm looking for a fairly advanced answer here. I know how to pop up.
When I'm out on my big board (a 6'10 x 21 x 2 3/4 - fatboy shortboard, not a gun or a learner board) which I use either on very small days for the extra volume or on big clean days when I want to get into the wave early, I've noticed a thing... yes, that's right... a thing.
I catch the wave, still a nice green face, pop up with no dramas, but then as I hit the board, I've noticed a slight bounce of the board, which stalls it ever so slightly and means theres a split second where it won't engage the rail or the fins. It makes the difference between getting onto the wall and ending up too low on the wave. This doesn't happen on my shorter or skinnier boards.
I'm aware that I tend to surf very centred on the board sometimes, so I think the volume is enough that when I hit the board it resists sinking and engaging the fins. Or, possibly, the board doesn't sink like I'm used to when I pop up, so I end up going too high over the board?
So you guys that ride bigger shortboards (at least sometimes - IB surfer?), or even longboards (Jaffa? ), where do you reckon the problem is. And what to do about it?
If one person says 'you should be closer to the front of the board', 'paddle harder', or 'practise your pop ups on the living room floor', I may well scream

When I'm out on my big board (a 6'10 x 21 x 2 3/4 - fatboy shortboard, not a gun or a learner board) which I use either on very small days for the extra volume or on big clean days when I want to get into the wave early, I've noticed a thing... yes, that's right... a thing.

I catch the wave, still a nice green face, pop up with no dramas, but then as I hit the board, I've noticed a slight bounce of the board, which stalls it ever so slightly and means theres a split second where it won't engage the rail or the fins. It makes the difference between getting onto the wall and ending up too low on the wave. This doesn't happen on my shorter or skinnier boards.
I'm aware that I tend to surf very centred on the board sometimes, so I think the volume is enough that when I hit the board it resists sinking and engaging the fins. Or, possibly, the board doesn't sink like I'm used to when I pop up, so I end up going too high over the board?
So you guys that ride bigger shortboards (at least sometimes - IB surfer?), or even longboards (Jaffa? ), where do you reckon the problem is. And what to do about it?
If one person says 'you should be closer to the front of the board', 'paddle harder', or 'practise your pop ups on the living room floor', I may well scream

