Re: False bottom still just damp
An alternative would be to go get a big jug of water, and slowly pour it all over that substrate (keep the jug moving, back to front and side to side). The goal would be to wet the whole lens of substrate to "field capacity" (look it up if you don't know it).
You may need 2 jugs for that large a soil volume. Just keep slowly moving the jugs, slowly pouring the water. Let some water run through the substrate, into the drainage layer. You will probably hear it if you listen closely. Once you get the drainage layer about 1/3 full, stop pouring.
Remember - the point of a drainage layer is that it makes it fairly impossible to over-saturate the soil. Anything the soil cannot retain just drains away. Now if you submerge the entire the drainage layer and make mud soup out of your substrate, you've screwed up. Stinky is on the way. Don't do that!
Keep your 10 secs 2x/day routine and observe the drainage layer for a couple weeks. If the water level goes down fast, I would up the duration, frequency, or both of your misting bouts. Probably would start with duration - take it to 15 secs. Repeat the monitoring and adjusting. Ideally you will get to a fairly steady state, wherein during dry spells the drainage layer might dry down some or even all the way, and in humid spells maybe it accumulates a little bit, but all in all it doesn't do much. Better a little too dry than a little too wet, but...you are so far from too wet, you might be pretty close to too dry.
Half my penny-worth, anyway...