Can tanks be too large?

[Bci]

Hi guys I am new to this forum and I have a question. It leaves the topic slightly but I didn't know where to post this. I have a boa constrictor imperator that I recently bought(3 months ago) shes is less then a year old and I'm feeding her once a week but planning to start feeding mayb every 12 days or so mayb someone could help me with that too? Anyways she always pooped about 2-3 days before next feeding but for the past 2 feeding I haven't been able to find any poo in her enclosure and am starting to worry a little( reason for joining) her current tank setup is in a 5'x2'×18" tall fish tank that I made a top for out of wood and mesh. It is a newly setup bio active tank with all live plants. If there is anyone who could maybe help me out I would greatly appreciate it as I love this snake it's a great reptile!

Also she is about 27-30" long. And her mice are always sized to the widest part of her fed frozen thawed.