The smaller 43mm fins will make the board a little more skatey, easier to swap over to toeside and you will lose a little bit of upwindability compared to the bigger fins.
I used to like the bigger fins, but found the smaller fins better for nearly all conditions, you just learn to adapt for the smaller fins.
Currently my Bronq runs bigger fins on heal side(53mm) and smaller(43mm) fins on the toe side, helps with toe side changes and general slashing around.
Wonderfulx.
If you're constantly catching the bigger fins in the shallows, then you need to get out a little deeper or swap down to the smaller fins. You're blaming the fins for you wanting to kite in watery sand, makes no sense.