dnd 5e – How should the house rules for tower shields work?

I understand that in D & D 5e, the tower shields are not technically part of the game, but the DM has allowed it. He has stated that it will work differently than a normal shield, but has not found anything yet.

I understand that this should be the job of the DM, but due to his inexperience, he has devised many house rules. He has a Dungeon Master Guide and the Player's manual, but still does not seem to understand the rules very well. The rest of the group had to help him so he could be a better DM, so any help would be appreciated.

Should the only difference between a normal shield and a tower shield be that the tower shield can be used as a cover if it is planted on the ground?

If it can be used as a hedge, would it be considered average coverage, three-quarter coverage or total coverage?