Is there a way to set target segment size in compaction/reindex

My Druid has huge amount of small segments which puts a burden to the server. So I need to reduce the number of segments by compaction or reindexing.
My goal is compact the old segments to 500mb in size for each. I saw that in the compaction/reindexing task config, we only have targetRowsPerSegment.
So even setting targetRowsPerSegment, the target segment size is still unknown, since Druid does not repeatedly store the same value within the same column and uses indexes. So if I merge 2 segments of 1mb, I could end up with the new segment between 1mb to 2mb.
Is there a way to set the target segment size instead? Or do I have to keep reindexing until the target size is reached?

Interesting one…

Have you done some SQL in the sys tables to SUM rows and size in the intervals to see what kind of thing you might end up with?