Two hits on being overweight.
1. Nasty fatpad, covering a large portion of penis length. This is akin to a pan with lard in it, and a stick standing straight up. The portion of the stick covered by lard is unviewable.
2. Blood circulation. With more flesh for blood to move, less blood flow thru the unit. Case in point, the many people here who got overweight, lost siginificant amounts of weight. Got all the BPEL-NBP difference + some, and stronger erections due to better blood flow.