Strange heaven fps behaviour

[Jon1]

I was doing some benchmarking in unigine heaven while testing undervolting and noticed if I focus on a different application on my second monitor my gpu usage and heaven fps go up.

EX:  focused on heaven I sit around 165fps and 45% gpu usage. focused on explorer or opera my heaven gets 300-450 fps and my gpu usage goes to around 75%.

I would expect gpu usage to go up if I went to another window but not for my fps to increase. Is it just because my gpu has to work harder so some goes to heaven or something else

 

EDIT: isn't exclusive to heaven, also occurs in furmark so I maybe I have vsync on somewhere? 

 

I might just be missing something, just confused and curious

Thanks