Hi Darcy and others,
Here's your post about Halcyon versions (#184 at the end of the Summer 2017 Debut! thread:
One of the differences between using Halcyon in a bag like the Synapse vs. the Luminary is the segmented structure of the Synapse pockets/compartments and the way that the S19 and S25 adjust to the way different pockets are filled. Notice that with the Luminary there's a (rather elegant) curve to the front of the bag that you can also see in the shape of the bottom. I'd imagine that this curved shape is elegantly maintained by the 525d Ballistic Nylon, whereas it would not be as well supported with a fabric that flexes more.
Just my thoughts, YMMV,
moriond