As far as I'm concerned, just like the influence of favor (2012 maj) or NF treasures or Zehtuka items, the more you go to the same places, or in the same campaign, without going anywhere else, without killing any enemies, the more your chances of getting rare items decrease. BUT, with the luck factor behind it, that doesn't change much... (like the favor, you get more gold items, but not necessarily good weapon stats, etc.) It's all luck, impossible to calculate mathematically or manipulate to your advantage. You can play 1 or 10 lotto grids, which increases your chances, but doesn't mean you'll necessarily win.
I've observed this after more than 40,000 open chests.
Edit: Don't forget that for the favor, this increases the number of rare items dropped, but not their stats. I drop more platinum wand during the favor with Halcyon's farm, but that doesn't mean they're more likely to be 20/20. A weapon's statistics have nothing to do with the chance of obtaining a rare skin. You definitely have to make a difference in this kind of discussion. At the time of development, I don't think they said that 20/20 on a wand was the best of the best and therefore had to be rarer than the rest, but the gold skin was. Inscriptions and Upgrade components have no hierarchy of rarity.