$FNMA $FMCC ackman's thesis historical basis - help glen

hey, can you help me figure out the historical context/basis whereabouts for where the g-fees tend to come in at? Ackman provided valuation ranges that are driven by the G-Fee basis... and I just don't know how that would tie back to any historical precedent.. please advise.

http://finance.yahoo.com/news/shocking-prediction-could-10-times-233406681.html