I found where you got your numbers. No matter what, pre or post cut, his salary is gone. No salary dollars would ever count in any instance if the player is cut. Only pro rated signing bonus.
http://overthecap.com/player/cortez-allen/1588/
His pro rated signing bonuses are $1.35M for 16, 17, & 18 = $4.05M total. This is the only dead money that can ever count against the Steelers, since the salaries are not guaranteed.
The Steelers elected to take the $4.05M total this year and it freed up $1.745M This is where the article gets it number for $1.7M in cap savings. This means 17 & 18 dead money for Cortez is reduced to zero. He's off the books after this year.
Post June 1st spreads out that $4.05M over multiple years. You still have to account for the same dollars.
Sometimes doing a little math can help understand why Omar would chose to take the hit this year. The FO is not as stupid as some of us might think.