Hello TD..
It is the plumbing under the engine that if an annular bypass were to have been used, would have no place to go but outward, increasing the OD of the engine.
I think if that were the case, the annulus could have been severed, into two separate axial ducts, allowing for the retention of the plumbing.
A better solution would have been to reroute the plumbing into the wing, around the annular duct. The annulus would not have to be much thicker in profile than the "pipes" themselves, the bleed accounted for 20 percent flow. Keeping the same depth as the pipes, an annular duct could have surrounded the case, and been ten times the cross section of the fitted bleeds.
The inventor rejected the ducting as "too heavy". In the patent......