I have heard you say you should always download a mag to allow seating on a closed chamber. I do run all my carbine mags like this, as I’ve found it required on the USGI mags that make up half my supply.
On my Glock mags, however, I have found them to seat without any extra effort when topped off. (They are mostly the slightly longer Gen4 mags in Gen2 and 3 frames.)
Have you seen any other reasons to download the mag if seating isn’t an issue such as feedlip stress, spring fatigue, etc?
Thanks and thanks again for coming through Connecticut. Your drills have vastly improved the efficacy of my time at the range and turned some friends on to seeking your instruction as well.