I generally attempt to push the encirclement at least 2 provinces BEHIND the enemy line. Once the AI realizes that it's being trapped, it begins an escape through the remaining gap, and if that's only a province behind them, they're each going to hold the door open for the next division as you attack each of them in turn, and they retreat OUT of the trap. The pocket needs to be deep enough to buy sufficient time to close the door before the long line of routers reaches it.
MOT is good for following up the tanks on the advance, with regular foot infantry holding and hopefully widening the shoulders of the encirclement, then moving up to relieve the MOT...
This is how I do it too. But I think my division structure is a little different to those used by most.
There are four echelons
The Break-Through. One bgd of your heaviest armour plus 2 or 3 strong but mobile Inf types + at least one support bgd. In this role, I often team HArm with Mtn and Mot-AA or Eng if there's an obstacle.
The Follow-Through. These want to be faster than your breakthrough divisions, but still pack a decent punch as they are likely to be fighting the enemy reserves in the "second" province. Typically [Arm+2/3Mot+SPArt] These will usually get the most aerial support as it's the second row back that needs to be taken as quickly as possible.
The Relief-&-Hold. These are your foot sloggers that follow on behind securing the provinces captured by the first two types. They don't have to be special.
The Leapfrog. This is the fastest unit you can make. It only has ONE purpose, to beat the other guy to The WIre. I typically use [LArm+AC] or, when available, [LArm+Mech]. As the name suggests, these small units will pass through your Break-Through & Follow-Through units to get to that all important (usually unoccupied) third province. They don't need to be particularly tough as (usually) they'll only be called upon to fight units that have already been broken.
Timing is very important. The Break-Through start first, often supported by some of your foot sloggers (from multiple directions for better effect) so they start moving early enough to reach their required positions. Give them orders to attack the second province back. (use Shift key)
Once the battle is in full-swing, you can order the Follow-Trough & Leapfrog divisions to attack the second & third provinces back respectively. This gets them moving early but it's important to ensure your frontage is full, you don't want these units to enter the first combat.
If all goes according to plan (and sometimes it does) when the first enemy units break, the Follow-Through & Leapfrog divisions will have already completed their movement in to the first province (without having entered combat, so no delay) and will immediately enter combat with anything in the second province. This is, as previously mentioned, where your air power needs to be concentrated. Breaking the
second province is what it's all about. If you break these units quickly enough, your leapfrog division will get to the third province before any of your broken enemy. This usually results in an over-run of the units in both first AND second provinces, which removes them from the game.
Now your foot-sloggers can move up un hindered to occupy the direction of your pincers and you can close the gap.
This technique works for me because I expend significant research on LArm Engines & reliability and let LArm armour & gun fall by the wayside in order to get their speed up as high as possible. Think Chaffee.
There are a few other research topics that improve overall speed, so I research them as well. A 16kph LArm unit may be crap in a stand-up fight (OK, it WILL be crap) but in manoeuvre warfare, they really work.
Incidentally, I've also found that HArm (even all armour) can take forever to regain Org while the Mtn (who usually have a lot more Special Forces researched and much higher Org) are ready to go again quite quickly. Is it gamey to have reserve HArm bgds to swap-in and let the "exhausted" HArm rest for a while?