As I said, I'm not a student of MP. But there are three measures of central tendency, and if the "value area" is constructed about the number of trades that take place at a given price, I'm assuming that these measures will be so close that any differences won't matter.
As far as range extensions, I believe that they are simply movements beyond the range, but there may be more to it than that. When they occur, of course, the distribution will no longer be symmetrical. It will be skewed. When this occurs, the
value area has likely shifted, as it did in the NQ on Friday. Whether it stays there or not remains to be seen on Monday.
There are plenty of MP devotees on this site. Shouldn't be hard to find more authoritative answers than mine.