[skyking]

the way the relative wind leaves a body has far more bearing on drag and lift than the way it arrives. In a crosswind situation the relative wind will stay attached a bit on the downwind side of a radiused trailer. I would speculate that this departing effect is not nearly as strong up front, in the shadow of the Tow Vehicle (TV), but more pronounced farther aft.
I don't think the flat face has any real bearing on it, compared to the aft downwind side.
A square trailer will have a long aft downwind side break that will cause a yawing force aft of the pivot(trailer axles) , in the downwind direction.
This force will steer the nose of the trailer into the wind, and consequently the nose of the TV downwind.
So that gust that seems to steer you so hard downwind in your truck is truly the "tail wagging the dog".
Now with your rounded trailer, this is not nearly as pronounced. That is why your experiences with the radiused trailers are what they are.
The relative wind over the downwind side stays attached just a wee bit better in your case. Because the trailer is radiused everywhere, it performs equally better in all conditions.
The wind does not push your trailer around, it pulls it around.