My brain kicked in and I figured out what I needed to do to make the Sprint mesh seat comfortable for me. It's all about adjusting the right seat straps.
On my Catrike 700 seat I keep all the seat straps as tight as possible and I'm comfortable. So I used the same strategy with my new ICE Sprint. I started off riding on the Sprint mesh seat with all the straps pulled tight. I felt like I was at the edge of the seat and my hip muscles would sometimes get uncomfortable (all the details here). So I played around with adjusting the straps under the bottom of the seat. Adjusting only the bottom of the seat made sense to me at the time. The seat still didn't feel right.
I started to give up. I even tried selling the Sprint. I had a buyer who was new to trikes but he backed out at the last minute. I took it as a sign from the triking Gods that I needed to give it another try. And then in a moment of clarity my 63 year old brain (almost 64) started to work and the answer came to me. I went down to the garage, took the seat off the Sprint and started making the necessary new adjustments.
Sure enough after adjusting the seat and throwing it back on the Sprint I rode off in comfort. Now comfortable I've been taking longer rides on the Sprint without any issues.
Why I didn't try this earlier I don't have a good excuse. I tighten all the straps to their max but loosened the bottom three straps behind the seat back (not the seat bottom). The third strap from the bottom is now a little bit loose. The second from the bottom is a little looser and the last the strap at the bottom of the seat back is the loosest of the three. The strap adjustment changed the ergonomics of the mesh seat just enough to resolve my issues with the seat. It allows my rear end to settle deeper into the seat. The adjustment also provides better lumber support. All is now good down south.