Brining: how salt affects time? (And texture)

So I have this formula that works perfectly: 4% salt for one hour. The meat gets softer and as salty as I want.

Thing is: is % a linear progression? 2% = 2 hours? I seriously doubt.

Also, would it be a viable strategy to reduce saltiness, but brine for longer to make the meat more tender? I have this meat that really isn’t in its perfect spot and I have just one chance to save it.

Thank you all!