Though I admit it may have been a function of level increase though. Given how soon after sanc comes I can't say I really bothered looking at say hero and keeping numbers to compare to see if level was the impacting force.
But given sanc does come realtively soon, I saw the general benefit of haven % as just having longer sanctuaries.

Though I did find if you use haven in the hero ranks generally you can get more people to fight with you. People won't know you have it up, which can attract an enemy into thinking they caught you without sanc and so maybe come at you. It is riskier to approach it that way since you're giving up sam dam redux and you may end up fighting someone who you really need it against, so not saying rely on haven heavily or even often at upper ranks.