Shield = cover

[Vidmaster7]

So say I'm wanting to home brew some shields. I think the way I want to go is have them give cover bonuses. what type of cover would you guys say for different sized shields?

[Kagerage]

+4 easy with some +2 +2 ref save and then one that grants total cover both ways. and then the random starter shield for +2 no ref save

[Vidmaster7]

say maybe +2 ac +1 ref for a small shield?
+4 cover +2 red for a tower sized or large size?