Tried looking for this answer with no success, so forgive me if it has been answered elsewhere within the forums,..
The problem here is that when the SSD starts reaching high capacities, there is no real way to get know what content is SSD and what content is HSM from user quota to decide how to better tweak the systems.
The HSM configuration parameters seem to be very extensive and one can really tune it to no end. But what does one tune to, if there is no proper data to go by.
zmprov gqu is very useful, how ever it just spits out user overall usage and does not break it down by message stores (store SSD , and Store1 HSM )
currently I run run gqu every day and use it to build a Delta of what new emails arrive per user , by subtracting the day before's value ( But this value itself is skewed as it takes into account new emails minus deleted emails, as opposed to just new emails. ).
Maybe I'm approaching this all wrong and should just set an attainment size limit and move content over to the HSM after a day, and not bother with details.