(for pure speculation and reflection)
Perhaps comparable with gcod and chod? (The first tha-dad-pa, the 2nd tha-mi-dad-pa...??)
But how? che ba is a verb (stative verb or verbal adjective) meaning “to be big” but chen po is an adjective, right? You are suggesting “enlarged” (gcen po) as opposed to “large” (chen po)?Rep
Surely g- serves a derivational prefix in both words. Can we find other words derived according to the same model?
I don't know what I'm suggesting. Perhaps just that the 'rules' for changes in verb tenses could have something to do with it. Those rules get so complicated, don't they?