[aerohead]

I've been looking into Jeff Howell et al.'s wake vs Cd 'linearity' claim.
Shooting from the hip, it appears that in order for this to be 'true' would require that their 'pre-boat-tailed' test vehicle had already achieved the flow deceleration-rate saturation point ,aft-body slope, and the actual tail surface was a simple, conical section of that slope, as a constant over the remainder of it's length.
W.A. Mair' boat-tail achieves saturation @ 44% of total tail length, and out to 100% of length, the drag falls arithmetically with reduction in wake area, along it's fixed, 22-degree slope.