Here’s what I do:

Remove top piece, heat mesh lightly and directly with a torch, immediately pour a pre-measured dose onto mesh. Replace top piece. Ready to go! (Try to avoid getting DMT on the glass sidewalls. What ends up on the sidewalls will probably not vaporize.)

Air flow may be an issue for the liquid pad – there may be regions that are so tight that hot air flows around them rather than through them. If that happens, there would be cool spots where DMT would migrate and be less likely to vaporize.

A screen on top doesn’t seem like it would accomplish anything. Your mesh would have to be VERY loose for DMT to fall through, and if it’s that loose, you probably wouldn’t have enough mesh to hold a dose – you’d get leakage.