Full-wave analysis, based on rigorous solution of the differential or integral form of Maxwell's equations, is too slow for all but the smallest designs. Traditional on-chip extraction engines are, therefore, being pushed to extract inductance and provide accurate high frequency interconnect modelling while maintaining computational efficiency and capacity. This paper describes further accuracy-improving enhancements to the commercial full-chip RLCK extraction engine, Assura RLCX, based on the return-limited inductance formulation. Specifically, we incorporate substrate losses due to eddy currents and power-ground losses while, based on design-driven assumptions, avoiding explicit extraction of the power-ground and substrate. Results are validated on small testcases where comparison with full-wave solutions is practical.