We have analyzed the effect of structural asymmetry and aperture position for field-effect transistor (FET)-based plasmonic terahertz (THz) detector with integrated aperture by using 65-nm CMOS process. By applying structural asymmetry between the source and drain in FET, we obtained 9.3 mV (7-fold) photoresponse <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(\Delta u)$</tex> in comparison to symmetric FET for aperture positioned at gate. In addition, by asymmetry in feeding the incoming THz wave with aperture positioned at drain, we have experimentally demonstrated highly enhanced detection performance followed by 18.5 mV (2-fold) <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta u$</tex> in comparison to aperture positioned at gate.