This was a concern we had as well so we did a fair bit of testing on versions with and without gaskets to measure the evaporation rate. The loss of IPA to evaporation was relatively marginal and there was little to no difference between the version with gaskets and the version without.
Archimedes principle is a bit challenging to contend with. To set the fill line, we averaged the bounding boxes of multiple prints and calculated the displacement accordingly. We’ll certainly take your feedback into account and the IPA reaching the top of the platform is normal.
The magnet that you’re seeing is designed to keep the lid in contact with the Z stage when the cover is lifted.