these are roughly the circumstances of induced drag suffered by low speed aircraft
but not aircraft in ground effect where the flow is contained by proximity to the ground
In ground effect the flow is straighter as the tip vortices are suppressed

I think an endplate and fences will contribute to straighten flow by limiting the transverse flow in similar ways.

Another way of dealing with the same issue is to reverse sweep the wing, which if too extreme will promote transverse flow to the root (deck) of the wing. For us this might make balancing the wing on a single set of bearings rather difficult, but it might be possible to influence the wake with a double reverse sweep tail, which would tend to suck air away from the tips.

It has long been understood that tails influence the mainplane after the thorough investigations into the mysteries of the Pou du Ciel Flying Flea crashes which later became related to other tandem wing aircraft

That aside, I believe the endplate the simpler to implement