We investigate the Gilbert damping constant α and the inhomogeneity of the effective magnetic anisotropy field HK[eff] in nanoscale magnetic tunnel junctions (MTJs) with various free-layer diameters D, which have two different structures possessing different magnetic properties around the pattern edge. Homodyne-detected ferromagnetic resonance (FMR) is used, allowing to disentangle the inhomogeneous broadening ∆H0 owing to the spatial variation of HK[eff] from the effects of damping in the linewidth of spectra. We find that ∆H0 increases with decrease in D while α is almost constant. The degree of the increase in ∆H0 is found to change with the MTJ structure. We show that these results are explained by a model considering the distribution of a demagnetizing field that increases with the decrease in D. The obtained findings provide important insights for the development of nanoscale MTJs with high reliability and high efficiency.