Currently the light leather armor (4.5 weight) and sarranid leather amor (4.5 weight) give +2, +2, +3 for each heirloom, whereas Nomad Robe (5 weight) and some of the other 4.5 to 5 weight armor give only +1, +1, +2. As a game balance issue there should be a natural cutoff rather than an arbitrary selection among the same weight armors of which get benefits and which do not.
Added a poll.