A reductant delivery unit for selective catalytic reduction (SCR) after-treatment for vehicles includes a fluid injector having a fluid inlet and a fluid outlet. The fluid inlet receives a source of urea solution. An injector flange is coupled directly with an end of the fluid injector and has a flange outlet in fluid communication with the fluid outlet of the fluid injector. The flange outlet is associated with an exhaust gas flow path upstream of a SCR catalytic converter with the fluid injector controlling injection of urea solution into the exhaust gas flow path. Internal surface structure that defines the flange outlet includes a conical surface joined with at least one radius surface. The radius surface is constructed and arranged to resist formation of deposits on the internal surface structure due to break down of the urea solution.