I don’t understand what you want to say. I know that there is no cover if you shoot at a target amd there is a difference of 3.
But infantry doesn’t have height 3.
And it doesn’t make any sense if the intervening terrain is height 0, but there is still cover. But because it’s a mathematical thing without any mentioning that height 0 is considered to be counted as not there, it’s still just a difference of 2. So you have to follow the same rules.