After some more test flying--landing and taxying particularly--I've come to the conclusion that the wind speed must go to zero at ground and sea surface. Because the slightest breeze can make ground handling of some planes a nightmare. Without differential braking, the plane has a wicked tendency to weathercock, and ya can't overcome it, eventually getting locked into facing into the wind.
It's too bad, because it's otherwise nice having a good crosswind right to touchdown.
I had originally made the wind 1/3 as strong on the surface as at 10m. No good. That's still to strong when the base wind speed is moderate or strong. And that 10m deep zone (a stock feature in the code) is too shallow for the purpose, because taller planes stick up into the wind where it's decidedly non-zero.

I deepened this transition zone to 30m, and as noted made wind speed fall to zero at the surface. Much Better! Now one can taxi in a strong wind. Why make things brutal for yourself, eh, when not all compensatory capabilities (like differential braking) are available? The deeper zone also makes for a less sudden change during T/O and LDG.
I'll advise when the new tweak is made available. I might see about adding another alteration or two in the meantime... maybe.
Stay tuned...