Over potting in S/H?

[Ray]

With 80% RH, drying too rapidly is unlikely, but if you're concerned, simply water more frequently.

The roots do not have to reach far down in the pot in order to get adequate moisture. They will eventually grow down into the reservoir, but that's a whole different subject. As an overpotting experiment, I put a 2" pot of Oncidium Sharry Baby into a s/h pot (converted florists cooler bucket) that was 12" in diameter and 20" tall. It grew and grew for about three years before throwing a couple dozen spikes and probably a thousand blossoms.

It's actually quite remarkable how long the LECA holds moisture. I went away on a two-week vacation once, and had my automated watering system fail. The tops of the pots were quite dry, and the pellets in the interior of the pot looked dry, yet were cool from evaporative cooling that was still going on, and the plants looked unaffected.