It’s Canon Now: Web Spell is a sphere, not a plane.

The question came up: for the Web spell, does the web itself fill a volume of space, or is it a relatively flat plane, like spiderwebs spun by spiders in the wild?

Initially, the plane configuration seemed correct; however, up reviewing the spell text, we come across this passage:

If you have at least 5 feet of web between you and an opponent, it provides cover. If you have at least 20 feet of web between you, it provides total cover.

The total cover rules state:

Total Cover: If you don’t have line of effect to your target (that is, you cannot draw any line from your square to your target’s square without crossing a solid barrier), he is considered to have total cover from you. You can’t make an attack against a target that has total cover.

Therefore, if 20 feet of Web is sufficient to provide total cover, it cannot be a flat plane – it must be a volume, a 20′ radius sphere.