Theory is good, but have you cut and pasted any? I have flown all the above wing tips except the winglet and let's face it, for RC work, except for maybe sailplanes, they don't work upside down and they'd get broken off the first time out of my garage in into my truck.

Also a buddy of mine made a rudimentary wind tunned and a wing covered n yellow Monokote that could have tips bolted on. We CA'ed red thread along the leading edge and tried different tips at various algles of attack.

End plates worked the best-they had no outward flow of the threads.
Hoerner tips worked well, but only in one direction, upright.
Square ends were next best with only a little outward flow.
Rounded blocks were next with noticeably more outward thread movement.
Stick type tips were next to worst.
Large, round tps like on 30's and most WW II planes except the Mustang and Grumman designs was absolutely the worst. The outward flow was extreme.

Next, we flew a plane with bolt on tips. End plates gave a lower landing speed and more resistance to stalls and spins.

I mentioned this in my column and several people duplicated the bolt-on tips. They all reported that end plates gave the same results on their planes, including a biplane.