Separate ISM policy for rollup index

So we have time series based index to store logs. index rolls over every few days or so based on size or age and that just works really well.
i am creating a continuous rollup on this index pattern and it was able to create a separate rollup index. but i see that newly created rollup index is getting larger and larger as we get more data over days.

i would like to rollover and have a separate ism policy for the rollup index. so that i can manage it separately from the source index. i dont think ism based rollup works for this. as there target index is static. can someone please help here