Interesting... This post illustrated how important the user application is to the preference of an angled versus a straight eyepiece. I've never mounted a spotting scope to an auto window, and never will in my hunting locations and use. I don't even own a window mounting adapter. This use is never considered. If window mounting while sitting in the vehicle was a large portion of my spotting scope use, I could see how that angled eyepiece could be advantageous.
Another difference is that when I'm backpack hunting, I never carry a tripod for the spotting scope. When hiking and on the move, binoculars or even my rifle scope, become the primary optic. The spotting scope is only pulled out of the backpack and set up after game is seen with the naked eye, binocular, or rifle scope. My spotting scope is then rested on a rock or the ground surface for a makeshift stable rest. I find the straight eyepiece to be more user friendly in this application. I can sight over the scope tube to get the animal into the field of view, then get the scope stable and zoom in. In addition, the straight eyepiece means less of my body is required to be exposed in order to position my head/eye to see the animal thru the scope, and much less motion and movement exposed to the sheep to get into position to spot. They say sheep have the equivalent of 8X eyesight, compared to the naked human eye. I don't know how that's been determined. I'd rate their eyes at 10-12 power based on my experiences, once the distance is closed to less than ~600-800 yds. Past 1200 yds they are less apt to zero in and go on high alert on even a walking human. But I'm more comfortable with less motion and less exposure when trying to confirm the age of the ram, or the length of the horn, because there's often two people moving into and out of position to spot, waiting for the ram to provide a good profile to confirm horn length.
Even when resting/sitting while waiting ambush/style for a game animal to appear off in the distance, my binoculars are my primary optic. The spotting scope is mounted on a tripod next to me in order to get a better look should I need it after locating game thru the binocular.
Not trying to convince anyone that my use and preference in a spotting scope is necessarily also the best for your use. Broz's description of use, and explanation of his preference for the angled eyepiece helped me understand why angled could be most convenient in his applications. And that caused me to note the difference in my use and application, and why the straight eyepiece has always been my preference.
As mentioned, a big consideration to me is when I'm struggling to get the spotting scope on an animal and time is of the essence. In those instances, I almost always find myself sighting over the body of the scope to bring the alignment close enough to find the animal in the field of view. This isn't as convenient with an angled eyepiece.
But I am much more comfortable with an instrument that sees the way I see -- straight ahead. It so happens the straight scope is also optically superior and that's based upon science, not preference 
