Reposting this from another thread since I’ve had to point this out so many times since people are under the impression that it does for some reason.
Quick tests:
Lv16 Wizard
vs Red Kepa (Lv12)
EXP Journal: 72 (53)
% Gained: 4.1
vs Vubbe Thief (Lv13)
EXP Journal: 110 (67)
% Gained: 6.3
vs Zignut (Lv28, +12)
EXP Journal: 144 (88)
% Gained: 9.2
vs Panto (Lv30, +14)
EXP Journal: 163 (140)
% Gained: 9.3
I have no idea what the red numbers are for, but if the green are ‘base’, there is no scaling. I leveled up just in case, and the numbers in the adventure journal for Panto did not change at all.
Lv17 Wizard vs Panto (Lv30, +13)
% Gained: 3.6 (equal to 163/4510 for next level)
So yeah. Farm wherever you want, low or high. You don’t need to stick to the same level monsters as you.
Edit: I have just taken note of a bug where XP does not correctly display in the adventure journal (killed a Zignut, one moment it showed as 28, another as 115) but the percentage gained still indicated the correct values.
Edit2: Hopped onto my Lv33 Cleric and tested, it became evident there is some sort of scaling downwards only, as Red Kepa gave me less than expected. Zignut and Panto remained static. Will work on exact values, but maybe this is where 5%/level came from.

