Mean power spectrum from the set of VIPERS mocks used to test the systematic accuracy of the model in recovering the cosmological parameters when including progressively smaller scales. The cosmology of the simulation is indicated by the horizontal and vertical reference lines, and the coloured lines show 68% confidence levels for different values of k_max. We find no indication of systematic bias when using scales up to k_max = 0.40 h Mpc^-1. Using k_max ≥ 0.50 h Mpc^-1 we find a degeneracy in the constraints. We select k_max = 0.40 h Mpc^-1 for our standard analysis indicated by the filled contour.