sorry, this was incorrect. it’s expected behaviour in tor/i2p-only node’s addrman that tor addresses can at max occupy 1/4th new table and i2p addresses another 1/4th. so that’s why we’re seeing only 1/2 the new table being fresh.
if we do the netgroup calculation - tor/i2p addresses have only 16 possible netgroups and only 256 buckets possible in new table (256/1024 = 1/4 new table occupied). see this writeup in case anyone’s interested.