For non-rare weapons, it's the area that matters, not the difficulty level. You can find higher % in say Normal Mine than in Ultimate Forest, just at a much lower chance. Too lazy to dig out sources right now ~~'
Not necessarily true, let's take the Normal Mine and Ultimate Forest Example.
In Normal Mine 2 when you drop an item:
2% for Native, 9% for A. Beast, 18% for Machine, 10% for Dark, 1% for Hit, 60% for nothing on each of the 3 attributes.
1st attribute will be Pattern 1, 2nd attribute will also be Pattern 1 while the other attribute will be Pattern 255 (i.e. can only be 2 attributes).
Pattern 1 specifically says:
8.97% for 5, 19.32% for 10, 38.52% for 15, 22.19% for 20, 9.98% for 25, 0.82% for 30, 0.11% for 35, 0.05% for 40, 0.02% for 45, 0.01% for 50, 0.01% for 55. (higher is not obtainable)
In Ultimate Forest 1 when you drop an item:
30% for Native, 19% for A. Beast, 13% for Machine, 8% for Dark, 5% for Hit, 25% for nothing on each of the 3 attributes.
1st attribute will be Pattern 2, 2nd attribute will be Pattern 1 and the other attribute will be Pattern 0. (so all 3 attributes can occur)
Pattern 2 specifically says:
4.02% for 5, 8.90% for 10, 15.32% for 15, 36.98% for 20, 21.26% for 25, 9.72% for 30, 3.31% for 35, 0.35% 40, 0.07% for 45, 0.03% for 50, 0.02% for 55, 0.01% for 60, 0.01% for 65 (higher is not obtainable).
As you can see, the difficulty does indeed affect the actual %, it's a combination of difficulty and area that affects the % drop rates, with Ultimate Ruins 3 / Seabed Lower / Tower / Desert 3 being the best (as they pull from Pattern 4 with the highest % drop rates). VH maps actually pull from higher patterns across the board, but the rate of actually getting a % is lower. (Ruins 2/3, Seabed, Tower, Des 2/3 can all get up to 90% untekked).