Tenting? I always set it to zero (in Altium, tag the "tented on X side"), which wholly removes the solder mask opening.
Such vias will sometimes have goo stuck in them, partially (stuck to the inside) or sometimes with small vias (<= 10 mil), fully (plugged).
I'm not aware that there's any advantage to setting the solder mask aperture to anything in particular. If you want to guarantee nothing gets stuck in the hole, you'd have to apply: hole radius + hole uncertainty + mask uncertainty = min mask opening radius. Which is typically 3+3 mil, or an extra 12 mil diameter -- as you're working with two of the worst dimensional alignments of the PCB fab. That's more than the minimum annular ring, so such a via need not necessarily be "tented" as such, at all!
Such an approach would help a little on larger vias, where you are able to conserve some space between nearby solderable surfaces -- a via between two connected pads, for instance (a solder wicking hazard). But I still don't think it's advantageous over a fully tented via, which should be unsolderable right up to the edge of the hole, and insulated until within a few mil of the edge.
Tim