I'd like to suggest switching the tier numbering so that it matches the ideal star ranking of the equipment for that tier. What is currently tier 1 could be broken into tier 0 and tier 1, tier 2 could be broken into tier 2 and 3 and tier 3 could be broken into tier 4 and 5. This makes it easier to remember which gear to wear where, makes it clear which gear will be nerfed where, and which gear will not be good enough where.
It could also provide a greater variety of starting depths, so a player with lower level three star gear could run tier 2 and 3 while a player with higher level three star gear could run tier 3 and 4. Or it could provide variety from gate to gate, with different gates having subtowns at different depth, allowing for longer or shorter runs.