I've looked it up.
lvl30 armor to 15 = 71 EP
lvl50 armor to 15 = 291 EP

I very much doubt 71 + 71 -> 291 will happen.

I combined a level 13 2-star with a level 1 uncommon, so:
lvl30 armor to level 1 = 0 EP
lvl50 armor to level 13 = 236 EP
result: 0 + 236 -> 86 EP (Snakeskin at level 7)