oh gosh, he is a puzzle!!! it's hard to say w/o the following PS - if the +12 had dropped back down to around where the AMPS had been I'd say the dose could be too high. If the PMPS was around the same as the earlier #s or higher, I'd say the dose was too low. Sorry not to be more help!
If you can get a PMPS tonight that might give you a clue, since the mid-cycle is in the pinks again. If you got a mid-yellow PMPS, I'd probably try 0.75 and see if the results improve. If the PMPS is in the pinks or higher, I'd try going up to 1.25.
Going back to 8/19 when you got a normal U-curve, that actually looked like this dose might be promising. Could be his body got used to it and wants more insulin, or I guess it's possible (though I haven't seen with many cats that lower doses work better, but ya never know) that after a few days, he's feeling like it's too much and is resisting the dose.
Are there any clues from his behavior? With Bix I can often tell some of that from how he's feeling - if the dose is too low you can see it, but if the dose is too high (even if the #s still aren't good), he acts like he's feeling better anyway. It's far from a reliable measure

but sometimes it's clearcut they aren't getting enough insulin - lots o symptoms cropping up - so that may give you a clue.
Since you got improved results when you went from 1.5 down to 1u, which is kind of unusual really, if it were me I'd probably be tempted to try 0.75 for a cycle or two, be 100% sure to get in at least a spot test or two as well as PSs, and see if you see blue #s again. I'm not sure that's the right answer, but given that you've already tried dose increases to no avail, might be worth a shot? With the caveat that I wouldn't stay at a lower dose for long if it clearly isn't working...