Excel: Filtering values and generating an average result

Hi

I am using a formula that will compare one value to the previous value in a column and ignore them until the percentage difference between them reaches a certain value, example
=IF(D17 <=$G$1,C17,0) G1 being the reference percentage

The resulting values I want to add together and average them and only stop when the values drop below a percentage of the highest value. I cannot seem to get this part to work properly.

Have uploaded a workbook as an example.

I am new to Excel.

Many thanks
Phil