Posted 04 August 2017 - 11:10 PM
I'm not a lens designer but a faster lens needs a larger maximum aperture, which in turn needs larger elements. The front element size is directly related to the focal length and maximum aperture (or more correctly the entrance pupil) but the rear element size as I understand it is determined by other factors as well, including format coverage and distance from the sensor plane.
But experience with lenses tells me that although larger format lenses are often physically larger (compare medium format lenses with 16mm C mounts for example), the rule is not hard and fast. I've come across tiny lenses for cine and stills 35mm and relatively large lenses (particularly zooms) for 16mm, and rear elements can be different sizes even for similar speed focal lengths designed for the same format, so individual lens design also plays a very large role.
As I mentioned before, modern telecentric lenses (more often "near" telecentric) designed for digital sensors tend to have larger rear elements than older designs to allow edge rays to hit the sensor more perpendicularly.