Formula to calculate weekly averages from another tab - dragging formula isn't working

I have daily production listed on one sheet. On a separate tab, I want to calculate the average for the week (Jan 1-7, Jan 8-14 etc..), but when I drag my average formula down, it skips to the next cell, not the next set of data.
ie: first cell calculates Jan 1-7, second cell calculates Jan 2-8 etc...
I've tried playing with an offset formula, but can't quite make it work..

Any help would be appreciated!