I’d think, having heard how a rowing shell for eights affects the tow vehicle, and I am extrapolating quite a bit, probably too much, but being careful here, that you would want the wheels fairly far back on that rig.
The kayak may have an aerodynamic shape that would oscillate. If the front deflects left, it could go that way pushing on the toungue until the toungue forces it the other way and the kayak catches air on that side with the moment at the center of the axle. If the wheels are farther back the side loading on toungue would be reduced. The wheels further back would have a similar effect as an aerodynamic tail weather vane.
My thought when I see relatively long toungues on bike trailers is that they reduce the leverage the load has on the trailer has to affect the bike.