A fast diamond frame (aka DF) road bicycle sizing has no adjustment on the actual frame. Comfort not withstanding, it is a simple, rigid structure that is laterally stiff , lightweight and efficient. For purposes of fit, what changes is the size of the frame itself(no hinged pivots, nuts or bolts) . The rest are not part of the frame, i.e. the length and height of the stem or length of the seat post
Unfortunately, the nature of a recumbent makes the seat an important member of the frame triangle i.e the seat stays the rear lower stays and the seat back. It's hard to have an adjustable seat angle without loosing some level of frame stiffness while adding some weight, no matter how minimal. For some, this is a small sacrifice to make for proper fit. For general riding and none competitive events, this is not an issue and hence the T50 and the QX100 can take some level of seat angle adjustments. I only wish that cruzbike had a unified front boom design similar to the Silvio 1.0 (without the suspension) for these utility bikes. But again, I understand it's difficult to achieve for more upright seat angles.
My take is, those new to cruzbikes(and recumbents in general), should start with an adjustable bike like the QX100 or the T50. They should tweak and mod it as much as possible over several months. Then once they adapt and establish a sweet spot they can choose a used S30 or a new S40 or a V20 depending on whichever will work best.
I guess, as the saying goes, you can't have your cake and eat it at the same time .... unless you had lots of money and get one custom built for you!
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