Magnetic cooling promises efficiency savings at room temperature but requires rapid cycling of a magnetic refrigerant in a magnetic field. Refrigerants with first order metamagnetic transitions are attractive but often a have dynamic limitation: a transition hysteresis that reduces energy efficiency in application. La(Fe,Si)13 seem to be a very rare material in that its first order Curie/metamagnetic transition is between magnetisation states in a very flat free energy landscape, which thereby removes the main mechanism for intrinsic hysteresis. Our proposal seeks to probe this energy landscape in applied pressure and magnetic field on WISH. We aim to understand whether hydrogenation, which raises the Curie temperature to ambient, preserves the theoretically predicted flat energy landscape and whether the magnetisation states remain quasi degenerate.