Will a drone drop to the lower preset RTH altitude if RTH is activated when the drone is already at a higher altitude then the preset? Or will it remain at the higher altitude all the way back to the home point?
Carefully read the manual. It will only ascend to the preset altitude, if the drone is higher than the preset it remains at that level.
But it is very important not to have any obstacles higher than the altitude the drone is returning home. You should care about that before the connection is lost or before you push the RTH button. The drone is returning at the straight line to the home point.