In my case my onwing all but told me after selection that he graded us differently
I've struggled understanding this. MPTS makes things extremely easy...you know what a 4 is, by definition. So if MIF is something less than a 4, and a prior time stud is doing something close to or at a 4, then they should be graded better, not worse. Honestly, I think some of it has to be laziness in learning the landing pattern definitions for a 4. Plus I think there's a little bit of "well, he/she's pretty good, so I'm going to challenge him/her..."
I get the challenge part, and I would do that for my on-wings that had prior time, but that's different than grading them differently. I was lucky when I was a stud and my on-wing flew on the side, so he would challenge me, and relate things to GA, but would still grade me as he would for non-prior time studs. And that was when MPTS was brand new. I guess that idea was pressed into me early on.
I've told this story before, but I had an on-wing that did very well through Contacts, making 4s early and would routinely make 5s towards the end. His FAM-12 he had food poisoning and got sick while we flew. His pattern work was below average for him that day, understandably (he said he wanted to rally and finish the event), and while sloppy, he was still meeting the definition of a 4 in the pattern, so I graded him appropriately (MIF was a 3 for landings, for that stage at the time...not sure if that's still the case).
I'll get off my soap box now.
I can only speak for my squadron/ wing, but the course that delves more heavily into instructional style is FITC. The FITU focuses on safely flying the aircraft first and the particulars of instructional style are mostly delivered one-on-one and certainly when a new IP asks for feedback and advice.
I can't speak to the T-6 FITU, but for WING 5, the T-34 FITU was a relatively quick NATOPS phase, followed by FTI contacts and RIs. This let the IUT get more practice in learning the plane while also learning the FTI inside and out. During those phases, you would talk about common errors and techniques to help studs (and the IUT). There would then be two defensive positioning/OCF flights where the IP would act as the stud and the IUT would teach and try not to prevent the IP from killing them. It was a good combo of training but of course the IUTs all wanted more of those "teaching" flights because it was good exposure.
Like KODAK said, there is then more one-on-one ready room chit chat once you're at the squadron where you can ask for advice, as well as get feedback from the SFS IPs after you send your on-wing on to the checkride.
I do think some squadrons were better at this than others, and which squadrons were better would change over time. The quality of the FITU helps too. When I was an IUT, the FITU was okay, but the flow was REALLY slow, which hurt learning the plane. When I was a FITU IP, it was better, but the quality of IPs being sent there were really hit and miss. By the time I left, the new OIC was doing a lot to change that as well as kicking the squadron OpsOs in the butt to help with flow. From what I understand, the place improved dramatically after I left.
Ironically enough, that OIC was my Primary on-wing when I was a stud.