If you can get a near perfect stack, when you decollimate the primary mirror reflections 1 and 2 will move away from P (the primary mirror center spot), leaving reflection 3 hiding (mostly or completely) behind P. Then you can tweak the focuser axial alignment by adjusting the secondary mirror tilt to carefully stack P-3.
I borrowed a Farpoint 1.25" Cheshire this morning, and a couple of the red triangular spots they supply with it, and installed one on the XT6 mirror. Recollimated to it and installed the AC. I think the red spot is not a good color for this purpose... I'm not seeing as many reflections as before, and those I can see are less clear. The inverted P3 reflection disappears before I can get it aligned under P. Plus, the larger triangular target occupies a bigger portion of the AC mirror face, leaving not much real estate to move things around and keep them all visible with the CDP technique. So it looks like, for now, I have to be content with pulling P3 under P as best I can and recheck the primary with the Cheshire. Does that make sense?
The white reflective spots won't arrive until mid-week with the replacement AC. I doubt they'll be smaller, though.