Help with Hop utilization and IBU calcs

[kegtoe]

I always seem to be missing hop bitterness, flavor, and aroma. My typical set up is a "hop spider" made with a stainless mesh cylinder from Utah Biodiesel. All grain beers. typically start with 7.5 to 8 gals wort to finish with 6.0 to 6.5 gal into fermenter.

My last IPA I had 8 ounces during the boil. with 2 ounces at 60 minutes. I ran this though a calculator and it says it should be 160+ IBUs. The beer doesn't taste anywhere near that hoppy/bitter.

Am I missing something with the calculator? Am I getting poor utilization with the spider, vs throwing the pellets directly in the boil?

Any help is appreciated. Below is my last calculating from BrewersFriend.

 

[day_trippr]

What's the diameter of the spider? And the mesh opening size?
Also, what is your brewing water like? Do you do any tuning on it for hoppy recipes?

Cheers!