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

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

I understand that this should be the DM's job, but because of his inexperience, he has developed many internal rules. He has a Dungeon Master Guide and the Player's manualbut still does not seem to understand the rules very well. The rest of the group had to help him so that he could become a better deputy minister. Any help would be welcome.

The only difference between a normal shield and a tower shield is that the tower shield can be used as a cover when it is planted in the ground?

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