the solution which you aren't going to like is to camp with a solid not mesh tent.
When we floated the Tatsheshini up in the great white north several years ago, many people were having this problem but glacial silt. It was easy to see the correlation between how much mesh you did or didn't have, and how much silt got in your tent.
Even if you only vents on top, the wind would lift it up under the fly to sift through the top vents. Ew.