Rick!
If this is the pic of your sled... I noticed that you have no aftermarket venting.
With just the factory "ducting" on the sled... I can see where cutting back on this area of limited airflow can see where you are talking about the
Possible "undesired effects".... but as Mike points out... those areas are mostly covered by the steering hoop/board-support tubing.
The exhaust smoke moving around those areas that you observed is probably from the very weak eddy-air-currents created by the spinning primary, since the sled is not actually moving a that point.... and none of the air that might move in the engine bay from the factory design is actually flowing through that area... just the "fan effect" of the spinning primary that goes away once the secondary starts spinning and the sled starts to move.
I believe that Mike is spot-on with his design.
With aftermarket venting on the sled...I see the possible undesired side effects being negated... to the point to where the stock airflow strategy no longer matters.