That would make sense, as it evaporates at the surface it would leave salts.
When facing indecision on which way to go I am going to do this three different ways and test results.
1) The way I described in my last description
2) The way
@Polyuro recommends with wick tube, screen, soil and fill tube
3) One with a shallow basin (made of plywood and poly) with a fabric pot sitting on a contained ring of pumice with a cover over water rez. I actually think I like the last one in theory the best, would make water level easily observable, clean out easy and by making it long and narrow for two plants to sit in. This gives you added surface area instead of providing more depth in a small rez, it would give less fluctuation in water level as it gets drawn down.