I've got a radrunner plus on the way for my mother to ride.

I was looking at the tricycle I bought her that she can ride but doesnt really like and noticed that the seat is set back from the pedals so your legs are more in front of you pedaling if that makes any sense.

I was wondering if anyone has used a layback seatpost on a radrunner and how it went?

I bought a radrover 6 for my mother with arthritic knees.  She wants to keep the seat low so she can plant both feet on the ground but then has trouble getting going.

She thinks its to big for her so I was looking at other options.  Has anyone been on both bikes?
Wondering if the radrunner 2 either is or feels smaller/easier to handle. 
Cant find any comparison pictures of the two bikes side by side.