Keep in mind, there's more to HANA memory utilization than just the data in the database itself. There has to be enough space to be able to process data the data as well. Check this out to see if it helps you better understand what's going on. It's a bit old but gets the basics across: https://www.edge-solutions.com/wp-content/uploads/2014/03/HANA_Memory_Usage_v2.pdf
And the SQL statements that I use most from note 1969700 are:
HANA_Configuration_MiniChecks_<pick your appropriate version>.txt
HANA_Heap_MemoryObjects.txt
HANA_Memory_Overview.txt
HANA_Memory_TopConsumers_History_Rev90+_ESS.txt
HANA_Tables_LargestTables.txt