personally I think its a figment of imagination. like the time someone at a party was telling anyone who would listen how went up in a extra 300 with ultimate high and did -6g.
Unlikely yes, but put someone who is up for it in the Extra and certainly possible - I have certainly had a few in the Slingsby that have done -2.5 no problem (also had a few that I have suggested a gentle fly around after two or three aeros of less than +4!).
There is the
Utter Nutter Flight | Ultimate High trip that will certainly push many people to their limit and give them some bragging rights at a party!
If this was a figment of the imagination or not, the question was asked "is this normal practice" and I was answering that.