The runners for the front seat (any version) mean that you can't put your feet outwards in the back, and to get a foot in a forward position you must put your feet together.
Now ... if someone is a little wide like me ... and doesn't like sitting on a long journey with your feet together (and therefore legs) then you won't like the back for long drives (like 60+ mins).
However my mother-in-law sat in the back for 4 hours straight (with rest stops on the motorway) and didn't complain, but she is like a stick.
This is the same on the F-Pace and E-Pace.
Basically if putting your feet side by side is unconformable for you or your passengers, and it's a MUST then the I-Pace may not be for you.
BTW for reference there is plenty of space under there is height so you can put you feet/legs forward a lot ... as long as they are together.
Hope that helps.