How to improve data hit cache maxdb 7.6

Hell experts

Iam trying to improve the system perfomance on ECC6 Maxdb 7.6.I have notce that if i start that database only my data cache hit rate is on 99%.on i start the sap instance it drops of to 92% even though there ar no users working on the system.So i think there is some tuning i need to do on the sap instance side.

Any ideas welcome