Just a thought here, but rather than giving separate, mapped contours different power settings, why not just number and color them as to their depths- 1 the deepest, 15 (or so) the shallowest. Color each countour differently, and line them all up in order in the software's color map. Give them ALL the same power and speed settings, which you'll need to determine --
then just do this: engrave color 1... then engrave color 1 + color 2... then engrave 1 + 2 + 3... then 1 + 2 + 3 + 4... etc etc...
I tried this once for 4 colors, MY headache was in separating the 4 colors -- but it worked. Once you get the speed and power dialed in so each cut depth is how you want it, should work...