One of the important parts you may have missed is not that you are just reducing your volume but you are doing so with extreme heat...one degree shy of actually leaving scorch marks in the pot.
This is difficult to do with a 3 gallon volume for most folks' equipment. Two 1.5 gallons starting volume, much more likely. Traditionally it would be done by adding items to the pot that far exceed 212 degrees...rocks, chunks of SS, glass, whatever.
FYI, a good 70/ is one of my favorite beers and difficult to find done well anywhere. I have only been successful once out of three tries. All three beers were good but only one got the right flavor.