We can't suggest if we don't know exactly what they look like.
Why not swap the power from your 2 first and 2nd rows to the 3rd and 4th rows since you said the company sometimes cuts the power? That's what I think would be the best option depending on their position or having an extra exhaust might work to bring the hot air out.
I think I can answer your question, in a 3-phase system, there is a limited amount of amps on which you can draw on each phase, you can't just move the load from L1 to L2 and expect everything to work unless the wirings are oversized, and by oversized, I mean doubled, it's also pretty damn stupid for the power company to cut just one phase at a time, it puts extreme pressure on their transformers, every transformer I saw is protected by a phase failure relay which will shut down the low end of the transformer when one of the phases is absent.
With that said you have two options:
1- Split the cold/hot side of the miner using a split room design, so you have a cold aisle and a hot one, you can use sheet metal, MDF or foam board, this will prevent hot air from entering the cold side as it will have to pass through the heatsinks of the "OFF miners".
2-Create a negative pressure zone on the exhaust side by adding an exhaust fan attached to the wall which faces the miners' exhaust fans, air moves from positive to negative, so even 2 rows off, the air will still go from the cold side to the hot side.
