I think you are correct about the height above ground being important - complicated a little by the shape of summit eg a “pointy rock” summit will help.
I have spent some time playing with a simple vertical antenna on 2m (wire Jpole made from 300 ohm twin).
Normally this is supported with the top of the radiator at 5m, but I have completed a few QSOs by holding the base of the pole as high as possible off the ground, eg raising the radiator by a further 2m. Without the raising, the calling stations were too noisy to copy. Typically I have done this on essentially flat topped hills, on several occasions.
Did you catch any of them sneaking into your cellar?