Count unique values if adjacent cell meets criteria

Hi all,

I need a little help with perfecting my formula. In the picture below, I need a formula in column E to count the unique occurrences in column A (excluding blanks) if its corresponding value in column B (B1 value) matches that in column D (B2 value). Currently column E is showing the values I would want the formula to return.
Capture.PNG

At the moment I have a formula as below:

=SUMPRODUCT(--(B:B=$D2),--(A:A<>""))

this will do a countif in column A if column B matches the value in column D, but would not weed out duplicates for me.

I need some help modifying my formula, or ideas on a solution. I have attached the sample workbook below for your convenience.

Book1.xlsx

Any help is very much appreciated in advance.

Many thanks.