Honestly? My fingers aren't that big, they just get cramped up in such a tiny space. For whatever reason (
So what is it you prefer about 19mm spacing? Do you have longer fingers or slap much? I wasn't blessed with long enough fingers to make it the extra ~ half inch comfortably.
When I first got a tight-spaced fiver, I thought it was great! I could play faster and cleaner, because there was less "slop" between the strings. But eventually, my RH fingers started hurting. As soon as I went back to 19mm, the pain disappeared (took a few days, though). When I try tight spacing again, the pain comes back.
I don't really slap on a fiver, I prefer to slap on a four so while I'm sure slap might be easier on a 19mm, that wasn't part of the consideration for me.
I'm glad narrow works for some of you folks, but for me it's just painful literally.

