rotary vs motion : velocity

I have a cnc router with a laser and a rotary axis.  I modulate the laser output (using the laserpower HAL) according to motion's requested vs current velocity, so the laser power is reduced during starts and stops.  Works fine for XY work.  For XA work, I'm running into the "which F" problem.  I'm using inverse time mode for the gcode but... how do I get inverse speed for the laser modulation?  motion.current-vel follows the F rule - it's inch/min if there's linear moves, else it's degrees/min.  If you do a coordinated move, you lose the angular velocity info.

In my case, I know the Z value will be "accurate" as far as "how far from the rotary axis are you" *in this case*.

Is there a way to do this in HAL?  Preferably without writing my own laserpower module

Or is there a better way to modulate laser power with a rotary axis?

Or should I just assume "it will work out" because the acceleration for X and A is synchronized, so reading either velocity fraction would suffice?