Does this seem like a reasonable cover rule?

[holywhippet]

According to the rules a creature gets half cover if there is another creature between it and it's attacker. But I thought about it and considered the following scenario:

CCC
A B CCC
CCC

Where A is the attacker, B is the creature providing cover and C is a huge creature being attacked by A. Under those circumstances B could hardly be providing cover since there is plenty of room around them to target C with.

So what I thought would be fair would be that B only provides cover for C is B is at least as large as C is. Does that seem fair?

[JNAProductions]

Yeah, seems fine.

[Rukelnikov]

Actually thats not the rule,

DMG pg 251:

To determine whether a target has cover against an
attack or other effect on a grid, choose a corner of the
attacker's space or the point of origin of an area of effect.
Then 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. If three or
four of those lines are blocked but the attack can still
reach the target (such as when the target is behind an
arrow slit), the target has three-quarters cover.
On hexes, use the same procedure as a grid, drawing
lines between the corners of the hexagons. The target
has half cover if up to three lines are blocked by an
obstacle, and three-quarters cover if four or more lines
a re blocked but the attack can still reach the target.

Emphasis mine.

As you can see, your example you could just choose one of the more convenient C squares ;)

[Marcloure]

Also, remember that the world is 3D. Thus, A can shoot over B and have no cover even if there were two other Bs blocking the way.

[holywhippet]

Actually thats not the rule,

DMG pg 251:

To determine whether a target has cover against an
attack or other effect on a grid, choose a corner of the
attacker's space or the point of origin of an area of effect.
Then 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. If three or
four of those lines are blocked but the attack can still
reach the target (such as when the target is behind an
arrow slit), the target has three-quarters cover.
On hexes, use the same procedure as a grid, drawing
lines between the corners of the hexagons. The target
has half cover if up to three lines are blocked by an
obstacle, and three-quarters cover if four or more lines
a re blocked but the attack can still reach the target.

Emphasis mine.

As you can see, your example you could just choose one of the more convenient C squares ;)

I was looking at the SRD for reference: https://5thsrd.org/combat/cover/