The larger bin looks fine
I can't quite see how they are joined or where the access is. The suggestion I'd seen for joining them was to cut the ends of both bins and weld them together with hot glue - but I guess that wouldn't work with separate sized bins. Assume you have things to add still but a bit less open space might go down well - eg more hidey places like an egg box with a hole cut in or a tissue box and a cardboard tunnel or something.
Is it escape-proof like that? Also the cut edge on the larger bin might be a bit sharp if they did manage to escape but could maybe just be sanded at the edges or something.
The first photo on this link shows two same size ones joined together. How big is the larger bin as it doesn't look too small.
https://www.google.co.uk/search?biw=....0.xWfUS51BqVI