In 1976 Browning came out with the BT-99 Competition with the higher rib, Monte-Carlo stock, and fatter forend compared to the beavertail BT-99s of the early 70's. American Shotgunner Magazine had a feature article that explained that the Competition model was designed to shoot 10 inches high at 40 yards. After 2 years Browning lowered the POI by popular request for the 'average' shooter. A friend of mine ran 300 straight in Singles and earned the 27 with his high shootin BT-99 even though some people said it shot too high.
Go to EBAY and search on BT-99. You may find an actual catalogue ad page for your model year BT-99. There is one on EBAY now for a *1979 ...and I quote the ad ... "at 40 yds the BT-99 is designed to impact 9", nominally, above the aiming point when using a stacked beads, figure 8 sight picture". The ad also says this is a "competition grade" gun and comes with a M/C stock and wider, competition-style forearm. I have a 1979 BT-99 ... but I have a conventional stock. So, maybe my gun isnt a competition grade. Mine shoots about 6-8" high at 36 yds with beads stacked.
* the EBAY lsiting describes the ad as 1979 .... but there is an insignia in the ad that describes the Browning "centennial" 1878-1978 .. so who knows. Maybe it is really a 1978 catalogue ad.