Wrong place?
In my opinion, you're mostly attacking the problem from the wrong end (of the can)
My Y piece made my remus, and my standard can, point at the panniers, with a resultant heat problem. I've got a set of Vern's
My mate has the same problem. His Y piece makes his Remus, and his standard can point at his Adventure Pannier frames, and has melted off the plastic retaining clip.
Nearly every y piece equipped GS we've seen has the Can pointing out wards slightly, and blowing either onto the pannier, the pannier frame, or the soon-to-be liquid indicator!
The best solution, and relatively simple... is to cut and weld the Y piece. Mine needed a 1/2" fillet putting in, and a wider spacer on the main hanger bracket, but that made it sit parallel with the bike and the exhaust jet pointing through the pannier frame without blowing onto the pannier.... no more heat!
My mates Adv just need two little hack saw cuts in the last bend of the Y piece... close up and re-weld the cuts + a wider spacer, and his pipe sat parallel too... which is what you need to achieve. You still need to know a good welder, but I think this is a lot simpler than the fabrication of all those pipes and deflectors.
I haven't got photos, but each bike would be slightly different anyway. Basically you just need to get the pipe sitting in line with the Panniers and not at an angle pointing at them.
Will