Grass runways cause FPS drop for Aircraft

Hi guys I am new on this forum so I am hoping someone can help. I have started
developing gliders for MSFS and so far have launched my first project, an AS33
Me. The biggest issue we have though that I cannot seem to find a fix for is
we get a massive FPS drop each time you use a grass runway. Its fine from
asphalt, but the moment you use grass it will drop from 60 to about 40-44. If
you then take off or land again in the same flight it will drop further to
about 20-25 FPS and eventually if you land and then take off again from a
grass runway in the same flight it drops below 10 FPS. Model is about 200k
tris and I have the environment occluder on the cockpit to block out the
grass. Removing the occluder does not help. Thanks Madolo