A method of operating a magnetic resonance imaging system (10) with regard to adjusting a radio frequency excitation field B1 to be applied to a subject of interest (20) to be imaged, the method comprising steps of—determining at least one position parameter (d) that is indicative of a position of at least the portion of the subject of interest (20) relative to at least one radio frequency transmit antenna (36) of the magnetic resonance imaging system (10) and—adjusting at least one radio frequency power-related parameter of radio frequency power to be fed to the at least one radio frequency transmit antenna (36) in dependence of at least one out of the determined at least one position parameter (d) and a determined geometric dimension (w) of the subject of interest (20) and—a magnetic resonance imaging system (10) having a proximity detection unit (46), including at least one proximity detector (D), and a control unit (26), wherein the control unit (26) is configured to carry out steps of such a method.
