Practicing less will make more progress?
Again I observe something strange. Since the start of the year I set my goal to be 'insane' and was doing 50xp each day. I managed to get to 39% fluency and was advancing by 1 point of a skill (not a skill) each day. The advance was slow because I was loosing a lot of skill points each day and after the 50 xp, I was merely 1 skill point better than the day before. This month I had to lower to 20xp cause I am busy. Now I am at 48% fluency and still advanced 1 skill point each day. I do less than half the work and have the same advancement but with extra fluency growth. I looks like duo's system intentionally makes you forget around the same amount that you learn.
Just like Usagiboy said, the fluency rating is for nothing. My fluency rating in German is 63% and in French 57%. In German I finished tree, went through it many times, got 30000XP, in reality I am about B2 level. In French I still have to finish the last third of the tree and only achieved 13000XP, I am hardly A1 level. You see now that the fluency rating puts me to similar level in German and French but my work that I have done here on Duolingo and my actual skills are very different in each language.