well, i'll take this one on, since i've been choppin on 3 different lexan shields since fall of last year, and i finnally have it dialed in.
my 883 sporty always buffeted really bad with the stock hd shield.
the same size as yours i think, so i pulled that sheet out of the mounts, and cut a much smaller piece and put back in. no need to tell you how that turned out.
then i cut a new piece 2 inches under sized, all around the shield, and got better but mixed results, again
so i got really depressed cause this was turnin into a 12 beer job, and i was no further ahead.
then i decided, yeh i know, brace yourself, to cut the factory 1/4 thick shield down to what i believe to be the correct size.
i removed 1 inch of lexan from the entire outer edge using my handy dandy ryobi coping saw!
tried it out, and
hit the sweet spot!
now i run 70 mph,and the air stream is perf!!
so if your brave! give it a go!