Well, since I think like a roofer 'cause I are one, might I suggest that you wrap the block and adjacent roof decking with ice and watershield, then flash out with the metal flashing . . . and then apply the final product on the chimney structure . . . . and forget about the 2" gap.
I would still leave a gap that allows water to clear, but it needn't be ugly.
Just my .02.
I would still leave a gap that allows water to clear, but it needn't be ugly.
Just my .02.