Index-Match Function Not Working all the time

[hoosierhunter]

Hope someone can help. I am losing my mind with this. I have attached the file for you to view. I have two drop down boxes which serve as the inputs to an Index function with 2 nested Match functions. The Index function works for the first 10 items of the "Largest Pipe Size" drop down, but does not work for any of the other. I have tried multiple versions of the forumla and formating the cells...nothing seems to work.

Here is my formula:
=INDEX($G$6:$P$44, MATCH($C$7,$H$6:$P$6,0), MATCH($C$6,$G$7:$G$44,0))

Any assistance would be Greatly Appreciated!!

Austin