Electronic switches built from single molecules such as biphenyl dithiol are promising replacements for traditional electronic devices. To support experimental investigations of molecular switches, charge transport values are typically predicted using non-equilibrium Green's functions constructed using density functional theory (NEGF-DFT). Previous studies of biphenyl dithiol, however, have usually overestimated experimental conductance values and have not reproduced a drop in conductance at low torsional angles. In this paper, we employ a methodology that constructs the non-equilibrium Green's functions from 2-electron reduced density matrix theory (NEGF-RDM). This approach has previously predicted lower conductance values than NEGF-DFT for systems where NEGF-DFT is known to overestimate transport. In the first direct comparison of the NEGF-RDM method and experimental results, we examine the biphenyl dithiol at a range of torsional angles. We evaluate both the quantitative accuracy of multiple NEGF methods and provide insights into the experimentally observed drop in conductance at small torsional angles.