Capping percentage of one cell based on percentage of another

I need to calculate a percentage in F39 so that the total in both F38 and F39 is 80% of the output (F35), up to a maximum of 90% of the annual consumption (F17).

The following code works fine when the annual consumption (F17) is less than the generation (F35) or not much more than the generation (F35) (see image 4000)

Please Login or Register  to view this content.

But when the consumption is (F17) is far higher than the generation (F35) it all goes wrong! (see image 10000). The total of cells F38:F40 should add up to 100%.

Please can someone help fix this so that the total of F38 and F39 combined never go over 90%?

Thank you

Also posted here - https://stackoverflow.com/questions/...f-another-cell
And here - https://www.mrexcel.com/board/thread...-cell.1176917/