Experiments have been performed on the JET tokamak with 2nd harmonic Ion Cyclotron Resonance Heating (ICRH) of hydrogen in deuterium plasmas to assess the role of finite Larmor Radius (FLR) effects on the resonant ion distribution function. More specifically, the influence of FLR induced weak wave-particle interaction on the clamping of high-energy resonant particle distribution is studied. The distributions of ICRH induced fast hydrogen ions have been measured with a high-energy neutral particle analyser in the range of 0.28-1.1MeV. By changing the electron density, the energy E* around which the wave-particle interaction becomes weak is varied. The effect of changes in E* on the distribution is experimentally verified for a number of discharges. Experiments have been analysed with the ICRH modelling codes PION and FIDO and good agreement with measurements have been found.