N-1 aerospike?

Anyone happen to know why the Ruskies decided not to go with an
aerospike, by tapping off some of the oxygen from the ring of engines
and dumping it into the base region or something.

I would have expected that they would have got good performance gains
from raising the base pressure.

But I read somewhere they thought they could get ~350 seconds that way
and get 10% more payload, but they still didn't think it was worth
it??? (But others said they got no more performance at all... and that
they seemed to be under target payload... the reports seem to vary
wildly.)

Anyone got a good story about it?