Do thicker rails also have an impact on a mouthpiece's reed friendliness? I've always found Doc's mouthpieces to be extremely reed friendly, while I find that some of my mouthpieces with super thin rails seem to be more sensitive to reed brand/cut/strength and can have a tendency to chirp more easily.
I think they do, and I think Doc expressed they did as well. Some mouthpiece makers prefer thinner rails, especially thinner tip rails (look at the pricier pieces available on the market--nothing exceeding .030" let alone .020" tip rails going on there). Too thin and mouthpieces can become chirpy, though other variables can trigger this as well. I can thin these things with the best of them, but I don't ever do it on my personal pieces (Partially because I'm classically trained and just like thicker rails). I generally like thick side rails and a thicker tip rail (greater than .030"). Tony Dagradi, one of my favorite jazz players, prefers tip rails I need bifocals to see (and use magnifying lenses to cut).
The frustrating element is meeting the demand of the consumer, who sometimes perceive thinner and tighter tip and side rails to be a cosmetic improvement over thicker tip and side rails and fail to recognize that the race towards super thin complicates things in terms of playability. They also sometimes feel it indicates the skill level of the maker). Doc didn't ever worry about this. He cut the rails the way he preferred them for his pieces and people just had to deal with it or not buy his pieces. If I had his acumen, strength of character, and wisdom, I would do the same. But I have kind of caved to consumer demand, which I often regret.
So, yes, they impact a mouthpiece's reed friendliness (as does too much of a tip contour). I love Doc's pieces. I am going to be producing all my dedicated pieces to him (10EJM--same thing as his Jazzmaster) with the thicker side rails without any alternative. I may vary the tip rail depending on a player's dedication to playing one reed brand/type).
All this talk about Doc makes me really miss him. He was so correct about so many things and so willing to share his knowledge with those who would listen.