[aerohead]

Subaru wind tunnel testing results from 1986 would give the aspirated rear bumper a 'fail.'
*There is no 'pressure' in front of the bumper.
*Subaru found the lowest drag when the bottom of the bumper was even and flush with the spare tire well in the floor of the trunk.
*A diffuser panel,even with zero slope would help guide the air from the rear axle area to,and off the bottom of the bumper.
*Cutting holes in,or raising the bumper only aggravates turbulence and drag.Measured to 3-decimal points.
*I put this data in the seminars so you wouldn't waste your time.