I believe you want to the bars to sum 100% every month, right?
The relative box will present the share of the value in the whole chart. If you have multiple locations and multiple months, the sum of all of them will be 100%.
You should uncheck the relative box and write the following expression:
sum (value) / sum ( total <month> value)
// you need to replace month by the dimension you are using as your time reference.
Hope this helps,