It fits with that better than anything else I've seen so far. The shape is somewhat different from what I got before:

Or maybe it only seems that way because my lighting setup has changed. I've emailed Rod.

You have to remember that you are working at/beyond the limits of the resolving power of your optical system -- rather like viewing something while closing one eye and squinting mightily with the other.

Also, the slightest angle adjustment can often greatly alter proportions and appearance. And last but not least, one has to deal with a certain level of variation within the species (even these small ones); thus for some linyphiids Roberts provides up to three separate drawings of the epigynum.

Compare your images with those here:
http://wiki.spinnen-forum.de/index.php?title=Centromerita_bicolor

I've got another epigynum image from A. Grabolle here that closely matches yours of the new specimen.

There may be similar Centromerita species in BC, or have you already ruled those out?

Some more drawings of C. bicolor:
http://www.araneae.unibe.ch/datasheet.php?taxon=Centromerita_bicolor

That's very true. A combination of the effects you mention could well be responsible for the differences I'm seeing. To compound matters, my earlier images were taken with a different lens now that I think about it too, so whatever optical distortions existed have probably changed.

The big one that is confusing me is the middle, "mountain-like" part (is there a term for it?) of the epigynum. I haven't seen a drawing or photo of C. bicolor where that's so pronounced and has such a wide, flat bottom.

C. bicolor is the only Centromerita species on the BC checklist (and the WSC has only that and C. concinna in the whole genus).