  The relative importance of the helicity and cross-helicity electromotive
dynamo effects for self-sustained magnetic field generation by chaotic thermal
convection in rotating spherical shells is investigated as a function of shell
thickness. Two distinct branches of dynamo solutions are found to coexist in
direct numerical simulations for shell aspect ratios between 0.25 and 0.6 - a
mean-field dipolar regime and a fluctuating dipolar regime. The properties
characterising the coexisting dynamo attractors are compared and contrasted,
including differences in temporal behavior and spatial structures of both the
magnetic field and rotating thermal convection. The helicity $\alpha$-effect
and the cross-helicity $\gamma$-effect are found to be comparable in intensity
within the fluctuating dipolar dynamo regime, where their ratio does not vary
significantly with the shell thickness. In contrast, within the mean-field
dipolar dynamo regime the helicity $\alpha$-effect dominates by approximately
two orders of magnitude and becomes stronger with decreasing shell thickness.
