The 3-4x multiplier for attackers assumes, I believe, that the quality of forces on both sides is equal. That's not the case here--Ukrainians have better morale, better training, and better intelligence. I also imagine that all of the new artillery and tanks being delivered, with better fire control, counter-battery fire, precision and/or airburst munitions, will also improve their chances. Will it be enough? I don't know.
One of the challenges of a Ukrainian counter-offensive is that their own supply lines get longer and the front will narrow, while the Russians' supply lines will get shorter. So the further they push the Russians back, the harder it will get. On the other hand, if they can push in the south far enough to cut off Crimea, and then drive a second salient through to Mariupol, they could create a nasty pocket of isolated Russians.