I dont terrible see the need as I dont terribly feel the issue as a problem - but here is how to solve it without losing xp or adding (much) xp.
Drop the streak as a measure for bonus xp.
a) Add +25% bravery bonus the first time you run a quest on hard if you havent run it on elite/reaper prior to that.
b) Add +50% bravery bonus the first time you run a quest on elite/reaper if you havent run it on hard prior to that.
c) Add +25% bravery bonus the first time you run a quest on elite/reaper if you have run it on hard prior to that. In this case you already got +25% on hard and now another +25% for a total of +50%.
Problem solved.