The authors report on midinfrared photoreflectance measurements of the band gap (E-0) and spin-orbit splitting energies (Delta(0)) in InAs-rich InAsSb and GaInAsPSb samples for varying antimony contents <= 22.5%. The E-0 behavior as a function of Sb content is consistent with the literature value bowing parameter of similar to 670 meV. However, Delta(0) does not exhibit the positive bowing of +1170 meV quoted in the literature: rather, a best fit to their data tentatively suggests a negative bowing of -225 meV. This result is likely to have strong impact due to the importance of the Delta(0) parameter in governing InAsSb-based device performance.