Events with t-channel single top quarks are used to probe effective field theory operators in s=13 TeV proton–proton collision data corresponding to 140 fb−1 recorded by the ATLAS detector at the Large Hadron Collider. To extract a maximum amount of information from these events, the joint fourfold probability distribution for four kinematic angles is simultaneously analysed. A method leveraging Fourier techniques to handle the challenges arising from this approach is employed. The relevant effective field theory operators are those sensitive to top-quark decay and t-channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions.