Range cover rules are silly

[Celanian]

400' tall Godzilla stands behind a 5' high and 10' wide car. He gets partial cover since an archer will draw a line from a corner of his square through the car to a corner of Godzilla even though the car barely covers any of Godzilla's cross section.

My fix:

Double size penalties vs range attacks. So a large creature would have -1 size penalty to AC vs melee and -2 size penalty to AC vs range. Size should affect range combat a lot more than melee combat.

Range cover cannot give more AC than the size penalty to range modified by how much of the target is actually showing. So a Large Ogre standing behind a table but with a Medium size cross section showing wouldn't get the full +4 AC. He'd get to cancel the size penalty to AC. Godzilla standing behind a car gets no cover bonus since a Colossal part of it is still exposed to the range attacker. A Gargantuan rune giant standing in water with a Large part of him showing can cancel the size penalty difference between Large and Gargantuan but no more than that due to cover.

[Some Other Guy]

Or, use logic and dictate that the attacker can shoot his bow at an elevated angle.

[Valantrix1]

Partial Cover: If a creature has cover, but more than half the creature is visible, its cover bonus is reduced to a +2 to AC and a +1 bonus on Reflex saving throws. This partial cover is subject to the GM’s discretion.

Note the second sentence. AKA, use your common sense.

[Celanian]

The example in the book has a sorcerer aiming at an ogre. Roughly 3/4 of the ogre is visible to the sorcerer and it is called out specifically as having partial cover. Even though the cross section visible to the sorcerer is larger than a medium creature, the ogre has a better AC than a human would have if they were standing at the upper right corner of the ogre position.

[StabbittyDoom]

I'm not so sure the cover rules are broken so much as not designed for 300' tall monsters.

And your house rule is needlessly complicated. Just rule that cover needs to cover at least 1/8 to be even partial OR that the attacker needs an opening at least as big as themselves. Godzilla can be half-covered, but a medium-sized foe still has plenty of room to target.

[Bob Bob Bob]

Creatures occupy the full cube of their size. None of them except the gelatinous cube actually do. The upper right half of the ogre's cube is probably 80% air. Dragons are even worse since the reach on the dragon's tail is just how long the tail is (so in theory you should be able to stab it from much farther away). Ditto the wings. The tarrasque, standing up, only leaves its ankles/feet within range of medium creatures with a sword. Yet somehow all of their hits can still inflict lethal damage to it. The size and cover rules are an abstraction, if the abstraction is not detailed enough for you feel free to houserule it.