According to answers to this question Wall of Force follows rules for area spells (PHB, 204)
A spell's effect expands in straight lines from the point of origin. If no unblocked straight line extends from the point of origin to a location within the area of effect, that location isn't included in the spell's area. To block one of these imaginary lines, an obstruction must provide total
Now, a hypothetical situation. Mage is trying to create a wall of Force in a 'sphere' mode around a creature. There are several possible variants and related questions:
Sphere is placed in a way, that wall intersects creature. According to description of Wall of Force – it causes creature to move to one side of the wall, caster's choice. Does it happen before or after area of spell's effect is calculated? I.e. does such moved creature leaves a silhouette-shaped hole in the wall or not?
Sphere is placed in a way that creature is within in. Point of origin is as close to creature as possible. Obviously some straight lines from point of origin to a some locations upon the sphere are blocked by said creature. For some of those locations creature is likely to provide total cover. Does it mean that Wall of Force would have holes in that case?
Wall of Force in a 5-feet diameter sphere option cast next to 6-feet tall creature. What happens with a creature? Is it forced to kneel or somehow else fit into the sphere or is it just moved, but still standing as it was standing, with his head and shoulders sticking through a hole in the Wall of Force sphere? What is sphere is smaller? I.e. is it possible to use Wall of Force as a trap, encasing only parts of creature and leaving the rest sticking outside?
In variant A and B, a creature doesn't cast a "shadow" in a spell's area of effect. As you said:
Creatures do not provide total cover; they provide half cover, as described in the Cover rules in the Player's Handbook (p.196):
So creatures don't block spell effects. You can't hide behind the fighter to avoid a circle of death, and a creature doesn't create a looney-tunes hole in a wall of force.
Cover is handled on a square-by-square basis, not an inch-by-inch or foot-by-foot basis. This is discussed in full in the Dungeon Master's Guide, p.251, with illustrations on p.250 and 251.
Variant C is effectively a duplicate of this question from a couple years ago, and answered thoroughly there. Personally, I would rule that when the caster selects which side of the wall to force a creature to, they can't pick a side that's too small for the creature to squeeze into, so you could use this trick to constrain a creature and give them disadvantage, but not actually harm them. It is of course possible to imagine a situation where both sides of the wall are too small (like if the creature is already squeezing and you then drop the wall right in the middle of the passage), so that doesn't make for an entirely satisfactory ruling -- but on the other hand, that's a really odd corner case that's unlikely to happen in actual play, and can probably be handled on the fly when and if it actually comes up.