Well, I know Campagnolo has a seatpost clamp that has a non-radial slot which I suppose will have some effect on the way the clamping pressure is applied ... or, it could just be a style-thing!?!
But, my carbon fiber frame has an aluminum clamp (CF seatpost) with a radial slot...
And, I have installed CF posts in traditional steel frames which only have the seatpost binder bolt ...
So, presuming your seatpost is the right size for the seat tube in your frame, I'm going to say that it doesn't make any difference other than from a cosmetic point of view.
I could be wrong!
So, if you're worried about crushing your seatpost, then you should probably get a different seatpost clamp.
Do two things(3 things). Keep the aluminum, turn it around 180 degrees so the bolt is OPPOSITE the slit in the seat tube and use carbon paste to install.
Carbon clamp is just dum, turning it around will keep the 'hole' as round as possible when tightening(rather than oval=cracks) and use paste to keep it from bonding into the tube.