I just did a SMaSH westy style with Pilsner malt and Idaho 7 hops. I did, (based purely on Brewer's Friend Mash hop calculation in the recipe editor), 30 IBUs of Mash hops. I tossed in that addition with 10 minutes remaining in the mash, stirred well, and put the lid back on and steeped for 10 minutes then began the lautering process. My hope was that it would have a similar effect to cryo hops in a way? Where you get the lupulin powder to run through the mash while leaving the leafy green stuff behind in the grain bed. Just an idea. Throughout the 60 minute boil, the only other addition was a 30 IBU [Idaho] 7 minute addition near the end of the boil, and a small dry hop charge with yeast pitch. The water was based on the Mosher West Coast profile, 200:50 SO4:Cl
This is all anecdotal, but it drinks really well like a West Coast IPA. I think the bitterness is just right on my palette, it's not overtly hoppy like some other westies. Brewer's Friend calculates it all at 60 IBUs and 6% alcohol. I really don't think I would be able to tell the difference between a 30 IBU addition at 60 minutes versus a 30 IBU addition mash hopped. Again, this is just my personal palette talking.
...and and. Brewers Friend says you need quite a lot more hops in the mash to achieve 30 IBUs than you would using hops in the boil. On this particular recipe, I'm showing 82 grams of Mash Hops to achieve 30 IBUs, while 82 grams at 60 minutes in the boil shows 150 IBUs. To get down to 30 IBUs i'm showing ~16 grams.