[Bug] Automaton Reinforced Chassis feat broken with potency runes

[Antmanton]

ItemAlteration in upgrade mode does not seem to be playing nice with armor potency rules on this item. Only the larger bonus applies with the out-of-the-box RE:

{
    "itemId": "{item|flags.pf2e.itemGrants.reinforcedChassis.id}",
    "key": "ItemAlteration",
    "mode": "upgrade",
    "property": "ac-bonus",
    "value": "ternary(gte(@actor.level,10),5,ternary(gte(@actor.level,5),4,3))"
}

Changing the ItemAlteration RE from upgrade to add like so produces the expected result:

{
    "itemId": "{item|flags.pf2e.itemGrants.reinforcedChassis.id}",
    "key": "ItemAlteration",
    "mode": "add",
    "property": "ac-bonus",
    "value": "ternary(gte(@actor.level,10),2,ternary(gte(@actor.level,5),1,0))"
}