A suggestion in the forums is to add a 1x1 slot to other armors:
https://forums.factorio.com/viewtopic.php?f=88&t=59850&p=368167#
--UNTESTED
data:extend
{{
type = "equipment-grid",
name = "1x1-equipment-grid",
width = 1,
height = 1,
equipment_categories = {"armor"}
}}
for _,armor in pairs(data.raw.armor) do
if not armor.equipment_grid then
armor.equipment_grid = "1x1-equipment-grid"
end
end
