Below a certain pitch, mask becomes almost useless, because the solder
will bride from pin to pin anyway. The challenge boards are 0.50m and
0.40mm pitch and neither has mask between the pins. What seems to
work for me is to just glob on the solder, then go over it with a
desolder braid where needed. That removes the glob on top, but leaves
the solder under the pin. This is with a 20 mil needle tip, not the
oft-recommended hoof tip.
PCB-Pool wants mask to be 0.15mm bigger, then they clarify that it's
mask size minus pad size. That means the gap between copper and mask
edge is 0.075mm (3mil). They also specify a minimum 0f 0.15mm
remaining between masks (6mil). That means you need at least 0.3mm
(12 mil) between pad copper to get a mask. I know I interpreted these
right because of two 0.65mm pitch parts on my other board, both with
"exactly" the minimum mask, one had mask between pins and the other
didn't (implying that one was a little off one way, and the other a
little off the other way).
Interpreting your data the same way, they want the distance between
mask edge and pad copper to be 4 mils, leaving 8 mils for mask.