I have a Monk with 25% dodge if I use nothing by my Dex score. If I add a passive that gives +15% dodge, the final dodge chance only increases to 36.2; with Mantra of Evasion active (which gives another +15% dodge) the final dodge change increases to 45.8%; if Mantra of Evasion is within three seconds of being cast, than it offers another +15% which gives a final dodge change of 53.9%.
Obviously, these are not additive percentages but I am having trouble figuring out the formula involved. What is actually happening to my Dodge Change when I gain +15% Dodge? If it helps, my Monk is level 56 and currently in Hell.