I have three boxes that are 30cm (app 12") wide x 30cm (app 12") deep x 25cm high (app 10"). My question is, will this be too high for my Brown Leghorns (who are apparently a cross between a normal size and Bantam )? We were thinking of cutting the front a little lower for it to get in. Also, how deep do you fill the container? I was thinking about 3/4 or should it be half?