Amount of gain needed for clear channels?


I was wondering if anyone has an idea (rough, or exact, either one) how much gain is needed to take a channel that is barely watchable to one that is stable?

The reason I ask is because I know what I receive now and I am not sure TVFools report is accurate for my location, since we can get a station that they say is -21 NM with about 80% strength.

So, if I have a station that breaks up briefly once a minute or so, how much more db gain will get it stable?
Or, if I have a station that stutters and breaks up constantly, how much gain would I need to make it stable?

I am not sure if this can be calculated or if there are to many variables and it has to be a guess, either way if you have any thoughts on how much more gain you would need to get stations like these please let me know.

Thanks! :)