I have recently updated my heads up strategy to implement a limping strategy. Basically, when stacks are in the 25 BBs range, the BB can shove profitably against your opens pretty wide and put you in a bad spot when you are opening a wide range. The pros who have adopted this strategy have done so as a defense against the 3 bet shove with these stacks.
From the SB, heads up I like to play up to 80% of my hands. If you are playing less than 60%, your are folding too often from the SB. But if I am min raising 80% that would allow the BB to shove 40%or more. So against this type of player, if you limp, they can raise, but they can't jam stacks this large, but then you put them into a bad spot with their raise as you can now jam over their raise.
Olivier Bisquet was one of the first pros I saw start to implement this, then I got some charts from Jonathan Little's book's bonus chapter on his limp/jam, limp/call, and limp/fold ranges.
If you are playing a straight forward player who is not exploiting your open range by shoving wide, then keep raising. I only make this adjustment against better players who are 3 bet shoving my opens wide.