D_Count vs Count giving different results when used in a custom metric

Hi! If I am looking to identify total tickets per active user. And when I use the D_COUNT function on the custom metric

COUNT(End-user submitted tickets)/D_COUNT(End-users)

I get around 7-8 submitted tickets per active user.

When I use the D_COUNT function on the custom metric

D_COUNT(End-user submitted tickets)/D_COUNT(End-users)

I get around 2-3 submitted tickets per active user. 

Is using the metric with D_COUNT preventing the same ticket from showing up multiple times?

I am trying to figure out what each result is telling me and which one most accurately represents total unique tickets/active users.