Apsidal motion discrepancy as a function of the orbital separation scaled with the q parameter. Each system is composed of a primary 1.5 M_⊙ RGB star presented in Table 1, and a secondary star with a lower mass. The stars composing the systems have the same age (2 Byr) and initial chemical composition (X₀ = 0.72, Z₀ = 0.010). Each colour corresponds to a secondary with a different mass.