Quoted from Flipper_McGavin:
Thank you for helping explain. With the big wheels on, I am unable to get the Escalera to pivot at enough of an angle for the stairclimbing feet to catch anything up onto that sill. I only played with it for a couple minutes so I'll practice more tomorrow.
In the situation you have pictured I would go as close as I could to the threshold and then tilt back to the big wheels and pull it over the threshold