It has been noticed by several players that the functionality of Caller's Bracers +1 and +2 work in unexpected ways. I believe the way it functions is that it first subtracts all perpetuation gear, then halves the remaining cost.
Example:
Naked
15 MP per perpetuation tick.
With bracers
7 MP per tick (-8 on hands)
With -5 perpetuation in armor choices
5 MP per tick (-5 on hands)
Compare this to Carbuncle mitts, that are always HALF of the max cost (say 10, wearing the mitts would make it 5).
Logically either carbuncle mitts are working incorrectly since they remove half of the MAX value, or the bracers are not working since they remove half of the CURRENT value.
The reason for this might be the day/weather requirement? Since it seemed that using Summonder's Doublet (or perhaps even Summoner's Horn) changes the reduction from the Caller's bracers.
I.e. your code probably looks like:
1) Reduce perpetuation fixed values
2) Reduce perpetuation based on weather/day
And the "half" portion of mitts come from 1) and "half" from bracers come from 2).