I have used the L and XL Makapuus a lot. The XL are a bit floppier but I think it is balanced thrustwise with the L because the surface area is much greater. The XL is floppy and big, they even can get a bend in them that will not straighten out which is very different than the board like stiffness of the L. They just take a little getting used to but they are good fins, just different.
Again it is perfectly normal, that is just how the XL is.
Oooh thanks good to know, that's one thing I was trying to judge, I can still catch waves with them but I felt like i was just windmilling my feet and not getting any purchase -- I am pretty seriously considering the reinforcing rods thing to give it at least a little more stiffness.
No problem, happy to see my Churchill knowledge of sizes finally was a help. It was strange for me too at first, then I found I needed to use my entire leg and keep my knees straight to get thrust. I found I actually got more thrust from the XL's due to the large surface area. They are floppy though and hard to walk in. The best pair I ever had was a lime green and black colored pair, they were perfectly rigid. The blue and grey pairs always seemed to be floppier. I have never used XL's for bodyboarding but I would imagine the biggest problem would be steering and using the fins as a rudder. There might be some spray on adhesives that you could spray over the fin surface area that would harden them up a bit, rather than trying to add rods. Maybe some stiff hair gel? I am not sure. Maybe If you sprayed them and then stacked some heavy stuff on top to keep them flat?
One thing is for sure your legs might be a little sore from using the XL because they are different, but they will strengthen. Every year when I switched from XL to L or vice-versa I would be sore for about a week.
I worked as an ocean survey swimmer for a few years we swimmers used churchill fins.
So I reinforced one of XLs and tested them out but I still hated them, adding a reinforcing rod along the side helped a little but they were just still really floppy -- I can see how they are good for long-distance swimming but they are not suitable for quick changes of direction / explosive takeoffs (i.e. bodyboarding) in my opinion. A lot of the time when catching a steep wave I may just need to make one single decisive kick which I just can't do very well with the big floppy fins.
Switched back to some other XL fins that came free with my apartment