Whatever you wish to believe, a 20 g is a small tank, especially considering we have no way to know if this is a 20 high, 20 extra high, or a 20 long...and there is a full 10 inches in length difference between those options. That will make a difference when keeping territorial fish. A 20 long is rather a different tank than other 20g tanks.
I agree, we don't know what the foot print of this tank is. Can we get measurements?