Andrew R Stewart 

Having owned what might be considered the grand daddy of the current recumbent era (an Avatar 2000) and serviced (then ridden) dozens more i feel i have a respect and understanding of the recumbent steering situation. I agree that there are a wide range of geometries. Having many packaging restrictions (and resulting tire sizes and steerer angles) and handle bar configurations (meaning the steering inputs and leverages are all over the place) it's no wonder that recumbent are so varied. Add the different use of the rider's body to help control balance and recumbent can be quite a handful at some speeds.

Your first post did focus on the rake as the variable, not steerer angle or wheel diameter. So please excuse us if we also focus on rake. And, yes, in most of our experience an 1.5" rake range is all that's going to be played with (35mm-72mm of rake).

It seems to me that some of your research might be with steerer angle or wheel diameter too so a bolted together fork might prove most adjustable. This way you could change just one part to change the fork's spec and continue to use the other parts. Along these lines you might consider having a bolt on drop out. This way you could just cut out/machine a different axle slot location and still use the rest of the fork. Andy.