Top n per month stacked chart

Hi

I am attempting to show the top 5 customers per month, based on the number of tickets they have submitted, over a rolling 12 month period in the format of a stacked column chart.

I naively thought I could create a measure that would do a distinct count of ticket id's, which could then be used as a value, with the Month-YYYY listed as the axis, with a legend of the customer name and limit the customer's to the top 5 based on the disctinct count of tickets. This has, in all fairness, done exactly as I have asked it to do, however, this isn't actually displaying what I set out to acheive.

It seems that the count of distinct tickets (ticket_count = DISTINCTCOUNT(ticket[id])) doesn't behave or belong to the context of each month, it is instead, getting the top 5 customers by ticket count (all time) and splitting their values by each date period.

I need to somehow create a measure that measures the top 5 for the month, in the context of the bottom 12 month rolling axis, as opposed to in the context of "all time". I would expect a different set of customers to be show each month, rather than the top 5 all time split by the month/year - the immediate outcome of this was that it was clearly not doing this as it showed the same 5 customers each month.

I beleive I need to use the RANKX function and somehow rank this by the month/year axis - I am just not sure if I am on the correct lines there? Any thoughts?

ds