In Is the DMG 3/4 cover diagram incorrect? the question asker points out the diagram shown in the DMG implies 3/4th cover, but it's possible to get a better angle on the defender meaning they only have 1/2 cover.
To determine whether a target has cover against an attack or other effect on a grid, choose a corner of the attacker's space... trace imaginary lines from that corner to every corner of any one square the target occupies. If one or two of those lines are blocked by an obstacle (including another creature), the target has half cover...
Is it mathematically possible to construct a scenario where only 3/4th cover is possible? Intuitively I can't think of a place to put the attacker in the diagram where one corner isn't able to get 1/2 cover by picking a better square, whilst still having some attack on the defender.