Ideal Gas Rosenbluth Weight Greater Than One

[ngantzler]

Hi Dr. Dubbeldam,
 
I am putting together a molecular model and have gotten an IGRW > 1.0. Similar models such as the PFOA model used in The role of surface thermodynamics and kinetics in the removal of PFOA from aqueous solutions give an IGRW~3.69 (T=298 K).

My understanding is that the IGRW = 1.0 for small molecules (e.g. butane) where we can neglect intra-molecular interactions; however, for larger molecules (e.g. octane) we expect an IGRW < 1.0, so I don't understand what it means to have a value greater then 1.0. 

Is an IGRW > 1.0 physically meaningful? What is the physical intuition to apply here? Could this be due to degenerate energy states?
 
Thanks,
Nick