Yep. I noticed this too. For me it's more along the lines of 75% full with a thinner juice like Reaper Blend. Counterintuitively, heavy VG juices work better when the tank is more full... maybe 85ish percent. Weird. Some fluid dynamics physics stuff at work there, I suppose (no idea, really... my Bachelor's degree and upcoming Master's are CERTAINLY not in physics). Most clearos, particularly the sub ohm variety, operate better with a small pocket of air, usually about 10-25% of the tank volume, and also ususally designed in by the manufacturer; they make it so that the tanks can't be completely filled... for the bottom fill variety, anyhow.
I just got used to this and only fill tanks about 3/4 full, just to provide that air pocket. The GS Air MS and M are a little picker than most... the Tank and the original, not so much.