The 16D is smaller, so it vignettes a little more. I've used the 16H on standard 8 cameras, and can get down to about 10mm for that format using prime lenses. For 16mm format coverage you might get down to about 20mm, but the front element of the taking lens needs to be no larger than the rear element of the anamorphic (about 44mm for the 16H, maybe 36mm for the 16D), and as close as possible, so a long hood for example will set the lens back and introduce vignetting. The anamorphic doubles the horizontal angle of view, so a 20mm ends up with the horizontal view of a 10mm, which is reasonably wide for 16mm format. I don't think a 16D would get below about 30mm (for 16mm format coverage) even if the taking lens was no larger than the 16D rear element.
Zooms tend to vignette more, I haven't got below 15mm (or 30mm for 16mm format) with the various compact zooms I've tried with the 16H. A short zoom range works better than a long one.
Long focal lengths aren't a problem (unless the front element is too large).