Near a wall, (CH) 66B>66A+B sometimes gets wonky (this happens for DNK too), but if you're doing the DNK version do stop immediately once you see a hit not connect or eat a punish.
Okay this is for playing against opponents familiar with the Yoshi matchup. For pressure setups, I know Signia does a lot of 6B>iMCF and 2K>iMCF (and of course, iMCF>iMCF) but 22K is actually a pretty decent tool too. I know the standard is to iMCF after this frame trap but people familiar with the setup will either backstep or block and wait for the iMCF. This is when you do a run-in grab or iFC 3K. It's a high, but under pressure very few people will attempt to TC and punish it.
3K is actually really good, I feel like people don't use it enough- it catches step slightly, does a slight pushback which still leaves you in iMCF range if the opponent tries to do anything, and is -6 on block. iMCF will beat out anything over i16 and people tend not to be as wary with 3K as compared to iMCF after 2K and 6B (outside the standard 4B/22K traps). Just throw out a 3K>iMCF first and observe how they react to it. If they habitually try to interrupt with a 2A (and most will try that or BB if they don't have an AS/NS B or JF twister, I guarantee it), 3K>backstep>3B whiff punish or 4KB. If they attempt to backstep after falling for the first iMCF setup, run in grab or 4KB. If they try to box step, throw out another 3K and reset the setup..
Yeah I just noticed 3K on block might be good place to iMCF. I do it after BB, 6B, and 6A, so why not after 3K? It was -8 in SCIV so it never felt like a good time iMCF then. Other on-block moves I might start doing it after is AA, 2B, 2A, 9B (lol). AA and 9B are -6. 2B is -8 and 2A is -7 but it leaves you crouched, so iMCF is a frame faster.
Though really, -6 isn't the best place to iMCF in a lot of MUs. The reason 6A and 6B into iMCF work so well is the the unfamiliarity of the moves -- they are pokes with short blockstun and low pushback. BB works because that move usually the "evade or GI setup" move; I have people doing evade-catching moves or delaying or moving and attacking and that's how I CH with that. A lot of mid CH moves are i16 as well, or mids just start to get strong at that point. That's ok because you'll trade, but you gotta be frame perfect!
Really, the key is to do -6 iMCFs when they don't want to 2A or BB (or if they're a slow character). And that's when you're:
-outside of 2A range, so they won't want to 2A.
-at a range you can backstep BBs or other fast mids, so they don't want to BB.
-outside of their AA or step-catching range, or at a range where you can backstep it. If you're within their fast-step-catching-zone, they feel more comfortable doing a BB, since they know you don't want to step, right? Though, if they actually AA, you'll CH them, so you might want that option available to them.
-not too far away or you won't CH their backstep catcher or mid-sidestep catcher and will just whiff and look dumb.
So if you want to attempt -6 iMCFs against Pyrrha or Mitsu, you gotta keep those subtle differences in range in mind. The spacing I'm thinking of is also a great place for them to dash-grab, which you will CH! For every other character, this spacing is a good place to 2A. The fact that you will CH slow moves that will actually reach you and be able to backstep fast moves that can interrupt you makes this spacing good for a lot of characters. Even if they decide to back up or sidestep, they will have a very hard time whiff punishing on reaction; they'd have to commit to a guess.
So, in conclusion, -6 iMCF requires frame perfect execution and deep knowledge of spacing and matchups to be successful, and it also helps to know how forcing fast reactions affects decision-making. Pretty much what this character is all about. Gotta have the whole package....