My bad! First, a confession: I don't own this jig, so take this for what it's worth (absolutely nothing!). I scanned through the DT330 manual online, and from what I glean the spacing between each finger is set at 1-1/4" (I conclude that based on the table on page 45 (section 7-16) of the manual, which says that even joints are multiples of 1-1/4"). Based on that, I drew a crude diagram of the joints.
Trying to wrap my head around the geometry, with the bits included with the jig, the size of the pin "base" (widest part) is determined by the dovetail bit, so is fixed at 1/2". With that, if my math is correct (and certainly open to criticism), theoretically the narrowest the tail would be is ~3/4" (1-1/4" minus 1/2"). I said in an earlier post that pins and tails would become more equal using thicker boards. I'm pretty sure, looking at the drawing, that I was wrong with that suggestion. To the contrary, the thinner the boards, the narrower the dovetail. My apologies!
That said, the only way I can see of making tails and pins about equal (bottom width) with this jig is to use a larger dovetail bit, and perhaps a commensurately smaller straight bit. For the D4R jig, Leigh makes 11/16" and 13/16" dovetail bits. Either of these would make larger pin openings. A smaller straight bit (7/16" or 3/8"?) should then result in larger pins. One way of fine tuning the pin size would be to place shims between the support board and your pin board, which will make the pins slightly narrower. Perhaps the people at Leigh can give you guidance before chasing down various bits. Due to the template side used for cutting tails, you are obviously limited to 8 degree dovetail bits.
Trying to visualize the geometry gives me a headache. FWIW, I feel your pain in having a tool/jig not meeting expectations. I was fortunate to find an older used version of the Leigh D4R, and while it does not allow table mounted routing, is really a nice jig to work with, once dialed in.
