I forgot to respond. Sry.

The two formulas are very close:

At 6 dB input, the first one equals exactly 2. Point (6,2)

At 20 dB input, the second one equals exactly 10. Point (20,10)

a^(x/b) is equivalent to (a^(1/b))^x so whether you change a or b you're just changing the base of the exponential equation (f(x)=c^x).

For any positive c, f(0)=1, so by changing the base you can choose one other point that the function passes exactly through.

10^(x/20) is the scientific standard, so I'd follow that.

2^(x/6) is a rare case where a and b are both integers

AND

a^(1/b) ≈ 10^(1/20)