Rexburg campus. If you line them up, campus to campus, actual academic buildings are about what you'd expect for a university that accommodates only two thirds that of BYU in Provo.
The other big differences are the Rexburg campus has very little on campus dormitories. Nearly everybody lives in all the apartments surrounding campus. A big chunk of the Provo campus is just the dormitories.
The other thing is the lack of sports stadiums due to Rexburg not supporting college teams. The Provo campus has a huge football stadium, a huge basketball arena, baseball/softball complex, soccer, volleyball, indoor practice facility, etc, etc, etc. Take those things away, and yeah. The campus will feel smaller.
I'm not sure what else to say. Nearly 20K students on campus is not small. It's not huge like UT-Austin (52K) or anything like that, but it's not small.