Hi! I registered just to respond to you since I don't have an XC90 but do have both an XC60 and S80, both 2015.5s and both have electric windshields, which I LOVE in the transition months! Beats blowing hot air on yourself when it isn't really that cold but you're fighting windshield fogging.
I have my EZPass installed on the driver's side of the CitySafe/rear-view mirror console tucked up in the corner of the glass (don't forget to leave 1/2" from the edge of the windshield). I originally had it on the passenger's side so I didn't see it, but I got multiple EZPass non-readings and notifications via mail since I had the license plates registered with NJ EZPass. (Make sure you register your cars and license plates with your EZPass provider.) I guessed that since some of the toll gates that I drive through where I was getting mis-reads have the reading equipment off to the left of the lane rather than straight overhead, the CitySafe/RV mirror was blocking the signals. I moved the EZPass transponder over to the driver's side and it seems to work great. Since moving it, I've only gotten one non-read, and that was at one of the high-speed readers on an interstate. Maybe I was going a little too high speed? Ha! I quickly got used to the EZPass being in the upper right part of my field of view and after a while I didn't notice it at all. I rarely look up in that area while driving for anything significant.
I just recently switched from EZPass NJ to EZPass VA because Virginia has implemented EZPass Flex, where if you have the required number of people in your car to qualify as a High Occupancy Vehicle (HOV) (three people on the I-95/395 and I-495 Express lanes, and coming soon two people on all of I-66 inside the Beltway during significant hours during the day) you throw a switch on your EZPass Flex transponder and you ride those lanes for free. In some of the areas, you can still ride in those lanes even if you don't have the required people to qualify for HOV, but you then must pay "dynamic" tolls via EZPass. Gets expensive during rush hours but it's worth it for some folks. Most importantly, ALL vehicles going on those lanes are required to have an EZPass--no exceptions. Having it on the passenger side of the CitySafe would have been very awkward to reach and then you couldn't see if the HOV switch was in the proper position, so it has actually worked out that it's where I can see it and get to it easily. The EZPass Flex is the same size as the old EZPass transponders (not the newer smaller transponders) so it's slightly more obtrusive, but the switchable functionality and free HOV use are worth it.
Hope that helps