The science and engineering of materials is, to an extent, expressed in terms of length scales and resultant interactions. The intrinsic nature of HEAs introduces an unexplored condition that is yet to be critically evaluated. To date, only a handful studies have explored grain boundary strengthening for HEA. In each case, extreme strengthening effects are reported. Some suggestions have been made which include higher friction stress due to lattice distortion, influences from dislocation curvature and dislocation glide mode. These may all be possible options; on the other hand, the physical interpretation of each constant within the Hall-Petch(HP) relation must be compatible with a model that accounts for such a contribution. In this work, the HP relation based on various models is evaluated through tensile testing, thermal analysis and work function measurements for a non-equiatomic Mn17Fe22Co24Ni24Cu13 HEA. Discussions aim to answer a fundamental question, “Do HEAs exhibit exceptional size effects?”.