DAX TOPN concatenate

Hi,
Can someone explain or point me in the direction of some clear information on how TOPN sorts things,

I've been trying to use it with Concatenatex to bring back for example the top selling item in the filter context in my example month,

it's not jus that my resultes are wrong I've put thng into DAX studio to try and figure it out and still cant see where some of the values are coming from.

So just to return to top value in the example for Jan and Feb to top values are from
so

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I would expect the table items to be sorted by hte sum of units descending, and then get the top but i don't .

any help on using this funcion welcome, i've attached the workbook i've been experimenting with to try an

I don't know a lot about DAX.

If you tell, what is your input and what is your expected result (and what are the rules to reach the expected results),
may be its easy to develop a formula without DAX. I think so.

You're filtering for the item with the top units, then calculating the sum of the units for that item. So for Jan for example, you find the largest units value, which is for item D, then you calculate the total units for item D in January.

Please add manualy the expected results in your sheet.