Thanks very much for this thorough post, and sorry about the late reply.
Well I must admit that later after my shave described above, I'm thinking it was probably a little closer to DFS than I realized, though still not fully there. So it really wasn't too bad of a shave.
My next shave was again with my Piccolo, using the other (new) side of the Feather blade. However this time I did my normal 2-1/2 pass shave, which is a full 1st WTG pass, then XTG on my face + ATG on my neck & under my chin for the 2nd pass, with another portion of a pass on the areas that are in essence a "planned touch-up". It really was an excellent pretty-much BBS shave. And fairly comfortable, too. I couldn't help but admire it.
While the "one-pass ATG" shave was an interesting experiment, I'm not yet convinced it's the way to go. First of all, it seems like it will take some multiple strokes or buffing. That's not really my thing. But also, shaving several passes in different directions seems to me intuitively better. Similar to the way sweeping a wooden boarded floor in multiple directions, does a more thorough job.
Now I do very much like the idea of one pass, in terms of speed and comfort. But in my mind, multiple-stroking or buffing the same area would seem to negate the comfort.
So who knows? Maybe I'll still try it (one-pass ATG) again from time-to-time. I probably will. But my next 2-1/2 pass Piccolo-Feather shave was really stellar. So I'm a bit loathe to mess with it.
Have you noticed on your Piccolo that the blade on one side of the head tends to show slightly less than the other? I have a Piccolo with the newer version head and it seems to favor this way of sitting my Astra SPs. Of course I’ve fiddled with it before and gotten the fit correct, but I’ve also come to appreciate it’s “off side” way of sitting also. I actually shave with it this way often. The “shorter” blade side I use in my care areas and the “longer” I use in my others. I still get BBS consistently all around, but the “shorter” side makes things a good bit easier and faster on my care areas.