Dependency: Separating dose frequency from damage frequency?

[Pursuivant]

I'm trying to stat out a creature which is ideally, "constantly" in contact with a substance on which it is dependent, but which only starts to take damage after a longer period, with a greater duration between HT rolls required to avoid HP loss.

For example, take a lungfish. Ideally, they're "constantly" in contact with water, but if they're taken out of water they can survive for hours rather than just minutes. (For sake of argument, ignore other adaptive changes like Amphibious, Breath-Holding, Fit, high HT, or Metabolism Control).

Any suggestions on how to "decouple" frequency of contact vs. damage rate if you don't get the required contact?

As a first pass, I'm thinking of halving the cost multiplier for Frequency of Contact (i.e., to x2.5, x2.0, x1.5, x1.0, . . .) and assigning an equal modifier to "time until damage after last contact". That leaves the basic disadvantage unchanged, if you link the current levels of contact time vs. damage interval, but allows for more variation.

[weby]

In most cases it is the "how often do I take damage" that is the determining value, as things like discomfort have no point value except perhaps at quirk level. So in such situations you should mostly just use the damage interval.