Percentile, ignoring date dimension for graph

Hi,

I have a data set for which I cam trying to calculate a percentile of the total values for a time horizon with the intention of then positoning it against the data in a chart to see which periods go above or below the quartile (percentile) for the full period of data.

Unfortunately the measure appears to change along each of the dates instead of remain constant... I assume this is something to do with it factoring in the date dimension table...

Data model (redacted - sorry - please let me know if any fields are needed) and measure below...

Has anyone any ideas?

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