The plasma stored energy as a function of input power follows an off-set linear law during ion-cyclotron resonance heating in the JET tokamak. The behaviour of experimentally obtained incremental confinement time tinc of centrally heated ICRH discharges is understood in terms of a local heat transport model where c0 a IP-1.2 and that <c> increases as the size of the q = I surface is increased at higher IP/Bt, or lower q, due to the presence of the sawtooth instability, where IP is the plasma current, Bt, is the toroidal field and qa, is the tokamak safety factor at the plasma edge. With the transient stabilization of sawteeth by central ICRF heating in JET, we are also able to assess the effect of sawteeth on confinement and determine the plasma current scaling of tinc without mixing its dependence on the safety factor. The same model is also used to explain the degradation of tinc when I CRH power is deposited off-axis.