Please, take notice of the framerate counter at the top right of the pictures below.
This first shot is a top-down view with all settings, including Unit Detail on Ultra. No DoF, Distortion or SSAO. Changing Unit Detail had no effect upon framerate from this angle.
This second image is a close-up view behind an Ashigaru unit with Unit Detail on Ultra.
This third image is the same angle but with Unit Detail on Medium.
This last image is the same angle but with Unit Detail on Low.
Loss of framerate on a zoom-in is normal, I understand this. But 30-45 FPS drop is just far too noticeable, especially considering how clunky and slow the camera becomes when zoomed in on the action. It's hard to watch something in the 20 fps range. It's also really odd to look at models that have less than 20 polygons and noodle arms. (exaggeration)