I believe this is exactly correct, and I've tested this somewhat. Sheeva's f+2, by the definition here, is a special mid, it says "high" but will get blocked when crouching, but only by a few characters, on most other characters it whiffs completely. I tested this on Kung Lao, and Sub Zero, and it just whiffed. But it has really weird properties on Stryker and Noob. If Stryker is crouching and NOT blocking he gets hit by it 100%, indicating that it's a "special mid" but if he crouch blocks it seems to hit him about 25% of the time. On Noob, he only seems to get hit by it about 50% of the time when crouching, and only about 20% to 25% when crouch blocking. On Noob also I've found that it almost always whiffs when he's in the corner, whether he's blocking or not, but still hits about 10% of the time. I've also found that the move tends to whiff more at close range. At first I thought this could be stance specific whether it hit or missed, since Sheeva changes stance while performing the move, but after testing it further, I've come to the conclusion that's it's actually just dependent upon where the character models literally are. i.e. character's "neutral" movement when just "standing still" will sometimes cause them to get hit by moves that would normally whiff, this is also true of standing characters, they may get hit at a more extreme range if they "lean" at any point during their neutral stance. Of course a human opponent will almost always be moving or blocking or attacking so this is probably not terribly useful.
Another weird character specific thing that works almost to the exact opposite of what I've found above is that Sheeva's neutral 2 will hit Stryker when he's crouch blocking 100%, but whiff 100% when he's just crouching, now this would appear to support something I read elsewhere on these forums which was that crouch blocking will make your hitbox larger than just crouching, and that would appear true in the example above, and it certainly is with projectiles, a lot of projectiles can be ducked, but if crouch blocking will get blocked. But I've found direct evidence above with Noob/Stryker and Sheeva's f+2 that some moves actually work the opposite way. What it really looks like is that you get hit when attacks strike your character model, and some people are "taller" when crouch blocking and some are "shorter" or that the "crouch blocking = taller hitboxes" was supposed to be universally true, but not 100% tested before the game was released.
What I've concluded is that "special mids" really don't exist in this game and it is just character specific, consequently it would appear that this game has hit detection much more similar to 3D fighters than 2D fighters which often use hitboxes much larger than the character sprite/model. This could be a pretty big adjustment for 2D players.