Responses to my thread "Hypothesis: Sit bone span equal to finger span"

(www.bikeforums.net/showthread.php?t=464117 )

indicate a huge variation in not only the width of what riders call their "sit bones" but,apparently, where they are measuring. References to "having us put our hands up our butts" make it sound like some riders are measuring way far back.

Various sources describe how to measure the gap in the ischial tuberosity. However, this bony structure is V-shaped (?) and the portion that is used in riding depends on the individual's position, yes?

In my case, I run a pretty significant saddle-to-bar drop (15 cm.) and am rotated pretty far forward, so most of my weight rests on the small, forward part of the V. Someone in a more upright position would put their weight further back. So, isn't it true that what constitute your true "sit bones" is dependent on the activity we are talking about?