For the sake of argument, let's say the following map is actually what is happening. I know most of you will quibble - and may, in fact, be right - but for the moment, let's say it is true.
Consider this a thought experiment. Humor me, please. The group as a whole has done so pretty well.
It appears the Ukrainians are aiming for clearing out the Russian troops around Kharkov and then pushing to the east. The objective - to my not so humble opinion - would be to capture the rail lines to hamper Russian logistics. The first of these would appear to be Vovchansk, imo. The others seem logical to follow if you look at the rail lines.
This would accomplish two objectives. The first is to cut off supplies to the offensives coming south at Izyum. The second force the Russians to pull back from those same offensives to prevent those supply lines from being cut. That would relieve pressure being placed by those offensives. That would buy more time: allowing for more equipment to move forward to the frontlines and training of more troops on western equipment.
How successful could the Ukrainians be by pursuing a logistics based strategy? Could it forestall an armored assault when the fields finally dry? Do the Russians have sufficient forces to drive back the Ukrainians from both the Izyum side and along the very obvious axis of attack along the rail lines? Could the Russians be forced into another retreat like Kiev and, seemingly now, around Kharkov?
Now then, take a step back, how do we set some falsifiable test criteria? How would we tell one way or around if Ukrainian offensive to take the rail lines was
actually happening?