Yes I think non-sequential mode is required as you are looking at multiple reflections.
We have a mixed-mode sample file under {Zemax}\Samples\Non-sequential\Miscellaneous\Mirror with hole, which defines roughly the geometry of a cell. But since the rays are reflected multiple times in the cell, you’ll want to construct it in non-sequential. You will find attach a simple system that can be a starting point. Let us know if you need further help.