Two ways of fixing that, add a wider treadle step to the existing treadle step that is distant (which is what actually makes it rat proof as opposed to the larger treadles) and/or block the sides with something, a board, concrete block, anything.
Thanks for the tip! We just got a new pullet to add to the flock and I don't want her scared of the treadle feeders. The block/brick idea will work for my situation when we're ready to integrate her outdoors.