LexxI'd like to know this formula as well, I didn't manage to deduce it by myself after reading that link. Hopefully @GentlemanJon is still around.
I can't remember exactly, a basic ratio produces weird results (i.e. obviously wrong) so I did something to produce a 'damping factor', but I can't remember what. Something to do with standard deviations maybe?
Anyway, although you'll be far more likely to take Kaidus's word for this over mine, it is largely a useless stat. There are a lot of reasons for this but I'll explain the most obvious ones.
Firstly the relationship between pocket (soldier, demo, whatever) and medic isn't one way, they have a duty to protect their medic as well. The better your medic is at staying alive in isolation the less this matters (in MiG this season in ETF2L Ipz had to play with Thun on medic who was very vulnerable and Ipz's stats were suppressed by having to look after him more), but the fact is that it's not simply a matter of getting heals to do damage. Players also get heals to protect the medic and get uber so the basic premise is excessively simplified.
Secondly, having looked at this in some detail a couple of seasons ago and not including it (I think I published my thoughts at the time but can't remember), when one team is getting badly beaten then it produces totally useless results because they never kill the enemy medic. The particular game with an enormous outlier was Epsilon vs CauseWeCan on Metalworks. Epsilon crushed them, Mike put in one of the most statistically dominant performances on Soldier it's possible to imagine, but because the Epsilon medic almost never died the level of healing he received dwarfed even that. Looking at the relationship between healing and damage/frags in the context of that game actually made Mike look bad despite being supreme.
So to look at this relationship you'd need to come up with something that took into account who was responsible for protecting the medic in a particular team and to what extent, how well the medic survives in isolation, and how well that team exploited their healing in relationship to getting uber and how much of a challenge the opposing team was able to mount and it's relationship to healing. There are probably other considerations. I haven't looked at this in detail because it's very hard, the sample size is tiny, and the chances of anyone else understanding it are zero and I generally investigate stats that I think will make reasonable reading or interest me.