Pat,
Seat comfort has several aspects.
The normal trade off of recumbent seats is between "recumbent butt" and
ergonomics. Many riders don't want to be real laid back. It certainly does
feel different. is hard to look back and takes some getting used to.
With the "Barnett Williams" type of sling seat, you run into the problem
of the fabric hitting the back of the thighs when you tilt the seat back
past the designed angle.
Many riders have reported good back results with a hard shell seat. But,
this requires a pretty extreme seat angle, so that you are, in fact, lying
on your back as opposed to sitting on your bottom.
Mark Stonich, a recumbent builder and designer of some experience, has
stated (if I've remembered correctly) that you need a seat back recline of
55 degrees from the vertical or more to eliminate recumbent butt.
You also need the bottom bracket to be in a reasonable position, after
your back is comfortable, to be able to develop some power.
Your Evox, IIRC, is a comfort bike of the new look. As such, you are
limited in how far you can recline your seat. You will soon reach a point
where you can't reach the steering. Changing the steering will result in a
lot of tiller. You will be laid back to where you can't push the pedals
with any authority.
Recumbents really should be designed as a system. The seat is only one
part of the system.
While the bicycle seat industry is a multi million dollar operation, it
has long been my contention that new riders buy seats and persevere in
riding through the discomfort. When their rear end stops hurting, they think
they have finally found "THE SEAT". It fact, they have more probably
trained to the point where they could now ride comfortably on a sharpened
fence post.