It's again dependent on range. You do have to move the Katy close to have a good effect. If it's firing from max range and I have a half track around I'll just reinforce and move around. If it is close you can move squads out after the first rockets hit as there is a delay and the area being barraged is smaller.
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Seriously, LefH is good against slow/static tanks and will easily finish them on low health as well as stopping repairs.
So lets choose Lefh over Elefant to counter a well microed ISU, lets change the meta!!! XD