For our KDP crystal orientation, various thermo-optic (TO) and relevant temperature-dependence parameters are defined, presented, and studied in the framework of a transverse and a longitudinal electro-optic (EO) modulation systems. This study is based on the concept of the so-called opto-electrical bias ([EQUATION] applied to the system. For both of the above EO-modulation systems, a set of original equations is extracted and investigated with regard to each of the more important TO or temperature coefficients. Using these equations, for these parameters the role of the transverse configuration is examined in comparison with its corresponding longitudinal configuration. A comparison is done with other orientation of the same KDP crystal.