To be honest I am not sure that it actually matters at all. Chances are that your DH wore cloth nappies that were wide in the crotch, and his parents certainly did, and I presume none of them walk like cowboys now.
If your baby is sleeping well, and there is no chafing or rubbing, then she is probably perfectly comfy. It is normal for babies to sleep with their knees tucked up, whether sleeping on back or tummy, so the nappy may not be impacting at all.
You could fold the prefods in quarters rather than thirds to make them a bit slimmer.
Personally I don't think I would be messing with a system that is working with no leaks