Exp Loss on Death calculations

Looks like you've mostly figured it out, but I'll copy what I put in another thread anyway as backup:

Never mind, I did some experimenting killing my storage mules.
Seems my base death loss is 5% (thought it was 10%??)
With Undead monster 'exp loss per death -2%', lost 4.9%
With Undead monster and S level Cannon Master card (-4%), lost 4.7%.
So the bonus for Monster life or CM character card is not x% off of the y% you would normally lose, but instead decreases what you would normally lose by x%. Probably wouldn't save a minutes worth of training in most cases.
Neither the undead monster life bonus or the Cannon master card bonus are worth bothering with.
Gosh Nexon, you are sooooooooooooooo generous.

The main remaining mystery to me, is why the base loss appeared to be 5% and not 10%. This was done on a level 5x mule with zero ambition.
Also I got killed on a low level AB recently, and I'm pretty sure I lost no exp, and it was not in a town or at a boss.

Edit: For those who like raw data:
Start 18.62%
Die with CM card and monster life bonus -> 13.92% (4.70% loss)
Die again, no CM card but with ML bonus -> 9.03% (4.89% loss)
Die again, CM card back again -> 4.33% (4.70% loss)