When we were making decisions about making the Carloo parts, we weren't sure they would all fit together, so we decided to err on the smaller side. This means that everything definitely fits inside of the external container and lid, but you may feel the edges of the external container when using the Carloo.
If this is uncomfortable for you, consider adding a "lift"!
A "lift" is something you put underneath the internal stainless steel container to raise it up so that the seat is higher than the external container.
We've had customers use different things as a "lift": cardboard, a diaper, a pet potty pad, a piece of an old yoga mat. A "lift" can be made of almost anything that's 1/8" - 1/4" thick. Ideally the material you use is a bit squishy so you can close up the Carloo with the "lift" inside. Like all the other parts of the Carloo, be sure to clean it as soon as possible after use (if needed).
We hope that Carloo LLC will be around long enough to make design updates to the Carloo...so that in a year or two, you won't need a "lift". But for now, we hope this helps!