A problem about Pulveriser Map Device

I bought Merciless Tharthan Executioner supporter pack yesterday because I love the timer of Pulveriser Map Device.
However, I found that the timer stops the moment I killed the boss.
This is a bit frustrating. The first step of my mapping strategy is to kill the boss first, and i'll find my timer stopped at maybe "6 kills ,0.18 kill per sec, 32sec finishing the map" and when I'm killing monsters, it just 6 kills.
I hope you can improve this timer, make it cooler!! I love POE and if you can make it happen, I'll love POE moremoremoremore!