Nope. AFAIK, monster level i.e the difficulty (HP/damage) increase when you move up in MP. The type of mob will be linear, i.e a champion/rare/white will all be based on MP level, all 63. Doesnt mean that you kill butcher (the strongest charactere at Act 1 = better chance of getting better gears) otherwise everyone will just go find specific mobs and  kill those only. As you move up in MP you gain bonus MF/GF and EXP. So, in essence, you get higher MF hence more drops at ilevel r63 rolls  which leads to a better "chance" of getting better gears. Thats what I understand le from their explanation.

TLDR More drops with ilevel63 rolls = better chances of getting good items