Wake Allowance

I have a nomogram for estimating tail plane efficiency.
Using the AR of wing and tailplane and a wake allowance,
I can estimate the tailplane efficiency.

From that it is a simple matter to calculate the neutral point of the plane, or the tailplane area required to achieve a desired static margin.

The problem is, I need some better way to estimate wake allowance.
The advise I have is to use wake allowance:

0.9 for a T tail
0.2 - 0.3 for a low position near the TE.

Are there some estimates in between, like moment arm 2*MAC or 4*MAC?

This would really help with new designs.

Also, are there and polars published with Cmo for symetrical sections with flaps at model RN values?

Then I can calc centre of lift to properly set up CG for stunt designs.