Use an Incline Bench for Foot-Elevated Split Squats
It can be a real hassle for someone who has limited ankle mobility to get to a reasonably comfortable starting position on rear-leg elevated split squats. Many debate between "squishing the bug" on the flat bench with their trailing foot (toes down), or instead positioning the instep down.
The best option is to make a simple modification using the very same bench you normally use. Simply set it up on a low incline.
The angle will conform perfectly to your instep and not require too much ankle flexion.
This also acts as a fulcrum for your shin to pivot around as you descend, encouraging a great range of motion.