TTC,
I get the prop-induced ground/water effect at speed, but the faster the plane the lower it must get in order to make the effect visible. As I type this out on my phone, I don't recall what I had done for v1.6 as compared to the further tweaking I might have done since. But I *think* I might have constructed the effect implementation such that as airspeed increases, the point in 3D space at which the effect is generated both moves farther rearward and moves farther below the surface. The result is to have the visible part of the effect particles become more diffuse and hence less 'intense' due to seeing just the top portions of them.
Try getting even nearer to the surface, and be sure the throttle is set so as to deliver at least 50% (I'd have to verify that figure) of the motor's maximum power output (not the same as 50% throttle setting.)
Are you getting the prop spray effect for float planes when taxying and at high enough throttle? If so then things should be operating as I have intended.
In my own view, the stock implementation of prop dust/spray is rather too exagerrated when the plane is off the surface. Once at flying speed, the motor's thrust vector is essentially horizontal. And at higher airspeed the rearward velocity component of pushed air relative to the environmental air is reduced. These two factors lead to a reduced surface effect, which is what I have striven for.
Let me know how your examinations proceed.
Glenn