Average of values in column with filter of rows (Dates) is incorrect if one variable has more rows (Dates) than another

I have 4 columns

Date Names Type Value

I want to calculate the average value by Name & Type accross a set of dates.

I've used the FIlter pannel to select the dates to cover (30 days in January. Note some Name & Type combinations have values for 30 days, and another has values for 3 months)

I created a column Mean based on the expression:

Avg(Value) OVER ([Name],[Type])

The results are fine for the cases of Name & Type with 30 days of data only.

For the case with 3 months of data, the result is the average accross all the 3 months of data rather than just the dates in January.

This happens even thought the data-table shows data properly filtered (only January data).

What might I be doing incorrectly?

(1) Answer