Medical Mastery Question

So, I'm looking at the upgrades I'll be making to my navi in the future, and while I'm sure this is okay, it's got me scratching my head as to its legitimacy.

Recovery-type navis have Medical Mastery, which adds 20% to all healing actions. Does this mean if I make a sig attack that heals 30 HP and costs 40 HP, wouldn't me using it techically make it a 36 HP healing action?

I'm sure this is exactly why recovery navis have this perk, I just keep feeling like I'm cheating the sig system.
That's perfectly correct. Improved recovery is exactly what the perk is meant to do, and that is the bonus you get with a recovery navi.

Each subtype has its perks; as a recovery navi you can't manipulate the weather, or gain improved A+ accuracy in something, you can't add free instances of break, or impact, or get a free range upgrade on your blast and nova chips and sigs, nor make free decoys of yourself or gain bonus damage on things that attack other things... You get more healing as your benefit.

The perks are all pretty balanced, in terms of gain effect, though with some a large part of it comes down to how you use them.

To be clear though, you still register healing things at the same cost and rate as everyone else; your bonus comes into play when you use them.

For example, you might register a signature simply as:

RefreshSig: (30Heal) 40pts, 1 TCD

When you use it in battle, though, might record it thus:

Action 2) RefreshSig: (36Heal (+6 subtype bonus), S) on Self.

Exactly how you record it in summary is quite variable, so long as you're clear on the maths.