How is miss chance calculated if a caster has Entropic shield active and is inside Darkness spell?


My question is simple. I have a warlock that has following invocations:

Darkness:

“This spell causes an object to radiate shadowy illumination out to a 20-foot radius. All creatures in the area gain concealment (20% miss chance). Even creatures that can normally see in such conditions (such as with darkvision or low-light vision) have the miss chance in an area shrouded in magical darkness.”

Entropic warding:

“A magical field appears around you, glowing with a chaotic blast of multicolored hues. This field deflects incoming arrows, rays, and other ranged attacks. Each ranged attack directed at you for which the attacker must make an attack roll has a 20% miss chance (similar to the effects of concealment). Other attacks that simply work at a distance are not affected.” Devil’s Sight: “You gain the visual acuity of a devil for 24 hours. You can see normally in darkness and magical darkness out to 30 feet.”

Devil’s Sight:

You gain the visual acuity of a devil for 24 hours. You can see normally in darkness and magical darkness out to 30 feet.

With entropic warding I get 20% miss chance on ranged attacks as deflection. In addtion, Darkness grants 20% miss chance if the caster is in it. If I am inside darkness and I have entropic warding on, do my miss chances stacks up to 40% (given I get ranged attack) or do I roll miss chance twice as twice with 20% with each roll.