Correlation matrix P defined in Eq. (50), obtained from the covariance matrix in a (w₀, w_a) flat cosmology, for an optimistic setting. Left panel: photometric survey combination, without cross-correlation. Right panel: cross-correlation term. The inclusion of cross-correlation between GC_ph and WL significantly reduces the correlation among the dark-energy parameters w₀, w_a and the standard parameters n_s, h, and Ω_b, 0. The FoC reduces from 1907 in the case with no cross-correlations to 824 in the GC_ph+WL+ case. This, in turn, leads to reduced uncertainties on all parameters.