Anyone know the formula to calculate magic damage dealt to a monster considering its magic defense?

Let's say that I deal an x amount of damage to neutral monsters using the bishop skill genesis. However, if the monster has magic defense of value y, how much minimum damage would I deal to the monster? I found these formulas on this website: https://ayumilovemaple.wordpress.com/2009/09/06/maplestory-formula-compilation/

Code:

Magic Defense
MAX damage = (MAX before defense) - MDEF*.5 * (1 + 0.01*D)
MIN damage = (MIN before defense) - MDEF*.6 * (1 + 0.01*D)

but I calculated it out and it doesn't seem too accurate (even the comments on that thread disagree). You can use this google sheet to calculate min magic damage (https://drive.google.com/open?id=0B0hEdoGbEe4wLXJXU0NiS1JnVXc) or use my app if you have an Android phone (https://royals.ms/forum/threads/magic-damage-calculator-for-android.88241/).

If anyone knows how to calculate the minimum magic damage dealt to a monster after its magic defense is considered, please post here. Thanks!

 

@Plenty

 

Magic Defense means nothing if you're at a decent level. The only thing that Magic Defense does is lowers the chances of hitting high as far as I've seen. Your minimal will always stay constant. You will never hit below it. This doesn't apply to early levels as much i.e. a Level 8 Magician using Energy Bolt on a Horny Mushroom, but during the end game, this will be a constant.

 

That makes sense, thanks for the explanation!