Encumbrance Formulas?

I was trying to find what I would need to get to the 25% mark with Scylla, so I compared differences between him and Charybdis, and finally reached the conclusion that ...

1 size = 1/35% reduction per pound of weight the gladiator has equipped
for example, if 2.75 lbs = 1% encumbrance, then an increase of 1 size would
mean that now 2.72 lbs = 1% encumbrance


So approximately 2 size = -1 encumbrance for most glads

What I am not so sure about is what strength does. I thought at one point 10 strength would negate about 1 encumbrance, but when I experimented with achievements, I had mixed results (because only a rounded percentage of encumbrance is shown, no decimal values to determine the exact effect).

Does anyone have their own thoughts on how size and strength effect encumbrance?

You seem to have better maths than me, all I know is size is more important than str when only encumbrance is concerned.