People want to be so precise. When you are dealing with living animals this does not always work out exactly the way you think it will. And I know I'm weird to a lot of people on this forum since I don't worry about a lot of things that they consider important. That probably comes from growing up on a farm with free ranging chickens. I don't see them as dainty little pets. We used chicken manure as fertilizer on hayfields and pastures. We used it in the garden too for a couple of specific uses.
My droppings board under the main roosts is the top of my 3' x 6' brooder, so it is 36" wide. I have two roosts made out of tree limbs that are not perfectly straight but are about 12" apart most places and 12" from the wall. I don't worry if I get a bit of wall splatter. Dry poop is not a danger, it will not smell. If it splatters on the wall it will dry out.
Occasionally a little poop misses the droppings board and hits the floor. It is a small amount and dries out in the bedding. The chickens mix that up with their scratching so I don't see a problem with that. The vast amount of the poop lands on the droppings board so I can scrape that off and add it to my compost pile.
Will some poop miss your droppings board and hit the coop floor since it is only 11" from the roost centerline? Probably but it should be a very small amount. Some would probably hit the floor if that distance were 12". I don't know what your coop and bedding look like so I don't know what kind of issues that may cause you. It is not an issue with my set-up and tolerances.
My juvenile roost is over my nests. Those nests are 16" so I get a line of poop on the coop floor in front of the nests. I don't worry about stepping in it, it will not hurt my coop shoes if I do but it is so close to the nests I generally don't step in it. When it gets thick enough I clean it up and put it in my compost pile.
I have no idea what your coop looks like. Mine is a walk-in with lots of access. You may have an elevated coop where you can only reach in. A lot of what I've said may not apply that much to you. But I do think you'll be OK with that pad 23" wide instead of 24".
Good luck!