Here’re a few things I’ve found out while playing Elite Dekaron.
The EXP factor varies from place to place. For example, in Frozen Forest lvl 40 it appears to be 60X, but in Heiharp lvl 25 it appears to be 40x. The DIL factor varies as well. To calculate the rate, watch the EXP and DIL drop for a monster and then do the math based on a Wiki like the 2Moons wiki which has a very nice Monster Detail section. Here’s the section for Heiharp.