I tok a stab at this using a=7, b=37 in which case the (n - 1) center piece surrounded by (f -2) + remainder (resulting in unbalanced triangles) still left room from the base (base is 3 for f2/8).
However, this could be filled with one d. Leaving the outside ready to be filled by nn + (2d - 1)*(n - 1).
So I tried again with a = 19, b = 61 and this time, with base = 8 (f2/8 and no remainder) it left 219 free cells, after filling in for n - 1.
However, if I filled in (n - 1) four times in the center the remaining slots could be filled by d.
It's been a while since I checked in so I'm a bit outdated, but I'm reading up on the stuff you guys have been doing and so far I'm blown away! Great work guys!
And, as always, great to see you to VQC!