sumproduct with date criteria and blanks in array

this is a bit of an odd one. in the attached sheet I have a formula in column D which is working out the following

Count how many dates in column A on sheet 2 match the month and year in the row on sheet 1 - There are 88 matches - However there are only 86 that have a corresponding number in column B
For those that match add up the numbers in column B on sheet 2 - this equals 1272
Divide this total by the number that meet the specified month and year criteria to give an average - this should equal 14.8 but the formula is counting blank cells in column B and including them and giving the answer 14.5 -

How do I amend the formula in column D on sheet 1 to ignore these blank cells and only work out the average for cells that have matching date criteria AND a corresponding number in column B? I have tried adding the <>"" at the end of the array in question but it gives value of 0 - see column E on sheet 1

Any help appreciated!
Thanks