I think the dwell-time is for the stationary part of the line, though, right ? I really want the power to be absorbed over a larger area than a single point.
Since there’s no built-in measurement of the line length (at least, that’s what I’m understanding), I think I can do it anyway, just by not using a spiral. Russ was using a spiral in RDworks, and he measured his line-length to match his calibration; I was trying to duplicate that. I’ll do a series of straight lines instead, then I can get a spiral-ish pattern and easily set the individual line lengths to add up to 16.3mm. Problem solved.
 To clarify what I’m trying to do: Russ covers it here and you can see the pattern he has the laser head go through to get the final exposure-time.
If you want to characterize the losses due to the lenses/mirrors in the system, it is in fact useful to be able to put all the power after the various optical stages, including the focus lens at the work-piece… otherwise I could just do a single line 16.3mm long.