how many shirts?
i usually do one of a few things on art like this:
print with a super translucent "darker" shade of the top ink and trap, but the trap effectively disappears into the shirt due to the translucency (extra clear or reducer), and the ink looks brighter due to the base showing through more than with an opaque top color (this really only works on black or similar colors or else the trap looks like a dark outline vs disappearing)
print with a super opaque (added white base) and lighter shade of the top color and no base. This works great with lower mesh, thicker stencil, and midtone shirts, but may not be opaque enough if there are also larger areas of that color or the shirt is fuzzier, or the print order required means you have to print the color earlier than ideal in the sequence.
Underbase with the thin line color or a shade close to it (or clear). small imperfections in registration will be less obvious than having white base poking out and top whites will still be vibrant when printed over another light color. we actually do stuff like this a lot, using a tinted base vs white, and it can really help with some of these fine line annoying types of art. We print tiny text on black with a clear base frequently and achieve what looks like 100% opacity on those inks and it looks really sharp.
