It looks like FFR has provided adequate hip and shoulder room for their concept of what the 818 is expected to be.
On the other hand, since this is most likely a street car, I would hope they would reconsider their frame design and make a few improvements while still at this early stage.
They really should provide better occupant protection and this means several easy modifications to the current design (assuming the frame in the video image, etc. reflects what they mean to build).
The main side protection member drops way too low toward the front wheel to provide meaningful protection in a side impact. Assuming there are no doors - a big guess, I know , the step over condition will probably allow for a side member at a generally higher level, especially toward the front. It should be widened at the shoulder too. Tied into this structure should be a vertical side member and CROSS CAR beam at the steering wheel support location (not just way up at the foot location). The new, higher side beam should be padded in such a way as to provide less of a concentrated blow onto the occupants, as well as allow several inches of space for deflection before body contact. This would be consistent with production car requirements and provide significantly better side protection than the current design. It would also provide a more roomy feeling too.
The higher side beam would also help in a front impact by resisting an intrusion into the upper dash panel area.
Any builder could make these changes on their own but wouldn’t it be better for FFR to do?