We need a serious effort putting together studies and hard data on the biomechanics of intercourse, compressibility of various tissues, devices to take fraction of a millimeter metrics on the exact dimensions of both male and female counterparts and some hardcore physics simulation software to derive the ultimate predictive formula based on probably several dozen factors that vary from person to person and parter to partner. Even then I don’t think this will be resolved - there will always be loons with a bee in their bonnet about some anal detail, it’s practically a philosophy. What next, quantum uncertainty for a fuzzy length measurement? :rolleyes:
In all seriousness, I believe if you define penetration from the point along the shaft at which the penis enters the bone ring of the pelvis, then even “grinding bone on bone” with a pair of anorexics is still going to result in a measurement perhaps even less than NBPEL.
So, if you are particularly obsessive about it, get out a permanent marker next time you fuck and determine exactly where you should be measuring from for a ‘fair’ volume.
Otherwise, if you are serious about actual PE - go ahead and grab a hacksaw to mark a notch on your pubis in which to dig the ruler in and pull as hard as you can. But then you will probably still hear somebody complain “But you’ve been working out therefore your arms are stronger and you can pull harder and that is what is resulting in the larger measure!”
Rant, rant, rant! :-Y