Table that calculates curtain folds based on 4 specific criteria

The attached file shows a quandry I am unable to fathom. It's a chart for calculating the points of folds across a curtain.

There are four fields:
LENGTH - the length of the whole curtain
FOLDS - number of folds in curtain (always has a half-fold at the end)
ALLOWANCE - amount to be deducted from LENGTH before any other calcs occur
DROP - the amount of fabric used in each "fold".

A "drop" of 25mm actually uses 50mm of fabric because it drops 25 and rises 25.

The sample sheet shows many examples of "results" on the left in the boxes.

The median is spotted, then folds are measured outward from there, up and down.

THE GOAL - the chart in tan on right must be able to calc the folds without the helper cells the samples on the left are utilizing. The YELLOW cells in the samples are what we want to appear in the red box based on the values entered there. The red box needs to be standalone, no lookups or references outside the box.

Thus I am stumped.

There is a second sheet where you can see some of my flounderings with the MEDIAN formula...

(Cross-posted here)