Only SF ability I know of is +1 range for ranged SF centers. I tried to figure out a melee SF unit's ability but after participating in 4 battles, I gave up. Every turn I hit different units, getting different hits. At the same time, I lose units which also affects how hard my SF units hit.
It seems pretty impossible to figure it out....
Since the dev team refuses to accept any request on revealing it, can they at least provide a way for players to make a good estimate on what their abilities are?