How to track device for specific campaigns?

Hi Everybody!

In the office, we have been trying to see which devices opened specific campaigns..
if we only use device dimension with the open metric, we can get it for all the campaigns ever released.. But how can I do that for specific ones?

For instance, in the image above I´m filtering the delivery for specific campaigns (for example the fall ones).. and I want to see the devices for them. But I want to see the total devices open for these 4 campaigns as in a sum, and right now I can only see for each one individually. Once I create a donut chart the devices double (image below).

So my questions:
1. Is there a way for me to see the total open devices for a sum of specific campaigns?

bonus question:
2. What Proxy means for the device dimension?

thanks