That much has been clear from your very first post. Whether or not the cover is depicting Arc Impulse or a regular dual tech has zero relevance considering that Marle does not use Fire magic on ANY of her techs in the final game, including Arc Impulse; no matter what Tech the picture depicts, it's obviously from the beta. I mean, as if the cover and beta screenshot showing the same monster and area combination that's not found in the final game wasn't a dead giveaway.
Oh my, you seriously believe that, don't you? You honestly believe Toriyama drew the final US cover for the game before the developers had started sketching the triple tech system. You also believe an illustration of these three characters fighting this boss in the snow, something that never actually happens in the game, was randomly drawn by Toriyama way ahead of time, then stored in a locker (it happens to be the one piece of Chrono Trigger art that wasn't released before the game; I know that because I obsessively followed the game before it was released). Finally, you believe that one of the very first and very few preliminary beta screenshots, taken and released months if not years before that cover, just happened to perfectly match that exact, final-game nonexistent composition by chance.
Jesus, the self-delusional lengths some people will go to avoid being proven wrong in a message board.
It's Chrono in the Japanese version. It was shortened for the western release as names could only be 5 letters long.