My Triumph is fully partially streamlined as per FIM rules with a tail that sticks 7 inches back from the tire. The wheelbase is three inches longer than standard. I am 5'-11" tall and sorta wide in the shoulders. It was not possible to get 7 degrees of taper behind the widest point and to have a reasonably narrow tail end.
The nose was made as blunt and rounded as practical so the wide part was as far forward as I could get it. This allowed for a longer tail taper. The sides gradually transition back at an increasing taper rate with the greatest taper, 10%, being right near the tail end. I figure, what the heck, it is too much taper but it is doubtful the air would be attached at the tail that far back, anyhow. Along the sides and forward part of the tail the taper rate is less than 7 percent.
The idea is, it is impossible to get correct taper everywhere on the tail of a short bike. The excess taper is put towards the back where it does the least harm.
Look at the pix on the DLRA website. Note Brett DeStoop's Suzuki water buffalo. That is a good starting point.