To me it’s an ever-fluctuating ratio. One day it can be 20 heal and 80 dps, another it can be 50 | 50. Evidently though as you familiarize yourself with an encounter, you will heal more efficiently.

In general, if you are actively looking for opportunities to squeeze in extra Glare/Broil/Malefix without letting your party mate die, you are in the right track for most part.

And then there’s another factor that shouldn’t be forgotten: the randomness that a human player brings, aka mistakes. There are just plenty of factors that affects this ratio, it’s hard to draw the hard lines. Perhaps in statics it would be easier.