It's based on version of Tibia Client.
7.4/7.6/8.0 as I remember don't have "summary hits" and all hits are completely separated from eachother
Newest Tibia Clients have summary hits that mean if you hit creature in same interval which somebody hits too (ex. in 2 seconds two guys hits one target with same type of damage) client will summary their hits and shows hits counted into one value.
It's not possible to change it by server-side you need to use OTClient to change it or do .DLL Injection to default Tibia Client. (It's complicated and I know only one guy who can do it @Qbazzz )