Comparing ROI taxed at ordinary income vs cap gains?

How can I demonstrate the performance of an investment that’s taxed as ordinary income to one that’s taxed at cap gains rates?

I run a small real estate investment fund, focused on flipping properties, and the returns are taxed as ordinary income.

I’m interested in showing our investors a pre-tax ROI that would be comparable to our investment strategy — if they went with an investment taxed at cap gains. This way they’ll be able to more easily evaluate those investments with ours.

I’m struggling with the calculation in red:

Here’s what I’m using for cell H30:

=(((1+(((H29-H18)/H18)))^(1/H21))-1)

And here’s what I believe I’m incorrectly using for cell H31:

=H30*((1-0.37)/(1-0.2))

Using the example numbers above, at a 37% income tax rate, our investors would receive back:

$20,127 x (1-0.37) = $12,680.01

Now taking this number as a constant (for what an investor would receive back after taxes), the pre-tax amount (with cap gains taxation) would be:

$12,680.01 / (1-0.2) = $15,850.01

However running the investment through compound interest calculators shows me the cap gains rate should be around 13.7% in order to achieve the $15,850.

This is why I believe my calculation for H31 isn’t correct.

How can I shape up my equation in H31 to property calculate this and help get the right info in front of investors?