Hammett ortho substituent constants?

 Dear Colleagues;
         It is my understanding that Hammett sigma constants are restricted
 to substituents at meta and para positions because steric influences on the
 functionality at C-1 (e.g., COOH, OH) cannot be clearly distinguished from
 electronic influences, whereas steric influences on the functionality at C-1
 by substituents in the meta or para positions is negligible.
         Has anyone ever undertaken (and pubished) a detailed analysis of the
 influence of ortho substituents in an effort to factor the influence of
 ortho substituents in to electronic and steric components?  I note that in
 the 1982 book "pKa Prediction for Organic Acids and Bases" by D. D.
 Perrin,
 B. Bempsey, and E. P. Serjeant Appendix A.5 is a small list of apparent
 sigma ortho values.  Does anyone know of a more recent and/or extensive
 lists, particularly ones containing values factored into steric and
 electronic components for benzoic acids and phenols?
 Thanks in advance to all responders,
 S. Shapiro
 toukie at.at zui.unizh.ch