Maybe a drop-thru style litterbox? Might be good for your 2 with their longer fur also. Ive not really seen suitable ready-made litterboxes that would allow poo to drop through a grate but still be comfortable enought for rabbit feet. So Ive made them myself using flatish style plastic grates. One I currently have is using the shelves of a plastic shoe rack. (see pic) But poo still gets flung.
It might reduce the amount but the downside is cleaning the grate.

Another approach would be having an “anteroom” space they go into getting in and out litterbox. Idea being any flung poos stay in the anteroom….hopefully.
Simple version: (this was posted by a member years ago. You can just see the entry in the cardboard box on the left.

Maybe a version of this but a larger space in front of litterbox with a mat to help trap stay poo’s? The pic is showing some still made their way out.
Or maybe they were left before bun went in…
Or, option three ( may not be practical..) – Get a rabbit friendly dog. They love cleaning up the stray bun turds. 