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There exists a collision bug where the check used to prevent Sonic from clipping on top of a surface he's too far below from isn't done if he's moving horizontally in the air. This can easily be seen if you put a solid object on a top solid surface and hit it from the bottom.

There are 4 collision modes while airborne, 1 for each cardinal direction. When he hits the rock, his Y speed is cancelled out while still moving right. Since he's technically colliding with the floor and the check isn't done, he clips on top of the surface, right into the rock.

This is what the missing check does, which is present when mostly falling downwards and less horizontally.

This bug also exists in Sonic 2...

...and Sonic CD...

Is this what lets you clip on top of the platform with the shield monitor at the beginning of Wing Fortress Zone?

If you mean like this, then, no. The clip is possible, because floor collision is ignored when he's moving upwards, and the wall sensor is too high up in this instance to trigger a wall collision. He also isn't deep enough into the platform for the depth check to cause floor collision to be ignored.

However, in Lava Reef Zone, there's a set of fully solid stairs that Sonic can clip into in the same fashion, but because he'll get stopped by the next step, he'll start moving down, causing the depth check to take effect, allowing him to fall right through. (GIF courtesy of Flamewing)