I assume you refer to the side door top and bottom. Firstly this is converter related not Fiat.
However the issue seems to be common with Auto-Trail, Elddis and Adria. Basically there's no trough.
I've an Auto-Trail and adjusted the tension to leave an acceptable gap. Trade-off is my dog uses it like a one off cat flap but doesn't rip it.
There are aftermarket options which will retain the edges but you then have a lip for trip and grit.
In Scotland the flyscreen itself doesn't stop midgies. Our bluebottles and cleggs are stopped as with lesser flies.