youtube.com/watch?v=_O0rsV4sG14
Pictures are worth a thousand words, what are videos worth?
By the way you don’t actually have to use the group dragging to get ships down there. If you’re careful you can deploy single ships in that area as well. I didn’t test if this happens on every map.
EDIT: Testing various ‘battle’ and ‘challenge’ scenarios this is occurring on every board to various degrees. Sometimes you can only move a ship a little out of the deploy zone, sometimes you can get it all the way down off the board and into the UI completely. It only seems to happen on the ‘south’ end of the map though, never the north, west, nor east.