Your supposed to fight on level in this game. That's why you get chains when you do. If you try to do a level that is 3 levels over you, you will just be taking so long that you could have completed two or three in the same amount of time and recived the bonus xp for speed.

Honestly, you should do the tier closest to your level even if your 27 you should do level 26. The bonus XP at the end of the leve will level you faster than the enemies inside the leve. Unless you are low on leves of course.