If you've replaced the m_y_cop uniform, I'd say the gap is to do with GTAIV referencing the bottom half from the rainjacket cop (it doesn't bother rendering the pelvis because the rainjacket covers it). There's some values in your pedvariations.dat file you'll need to change to override that but I'm not sure off-hand exactly how it's done.
m_y_cop_traffic and m_y_strooper are the other uniforms in regular rotation.