Difficulty level: Need help on Enemy at, Challenge, Cboost

[John Robinson]

1.) What does, Enemies at 80%, Challenge 90%, and 20% Combat boost mean?
2.) Does it have anything to do with enemy captain level vs your captain's level?  Does it limit which Talents the enemy captain can use. 
3.) Could I get one or two specific examples?

Difficulty Levels:

Basic
Crew	Capt/Officer No Death	80% Crew Death Save	25% Bonus Profits	40% Bonus XP
Enemies	at 60%	Challenge 80%	25% Combat boost
Normal
Crew	Capt/Officer No Death	70% Crew Death Save	20% Bonus Profits	25% Bonus XP
Enemies	at 80%	Challenge 90%	20% Combat boost
Challenging
Crew	Capt No Death	60% Officer/Crew Death Save	15% Bonus Profits	15% Bonus XP
Enemies	at 80%	Challenge 100%	15% Combat boost
Demanding
Crew	Capt No Death	50% Officer/Crew Death Save	10% Bonus Profits	10% Bonus XP
Enemies	at 100%	Challenge 110%	10% Combat boost
Hard
Crew	Permadeath	40% Death Save	5% Bonus Profits	5% Bonus XP
Enemies	at 110%	Challenge 110%	10% Combat boost
Brutal
Crew	Permadeath	30% Death Save	0% Bonus Profits	0% Bonus XP
Enemies	at 120%	Challenge 120%	No combat boost
Impossible
Crew	Permadeath	20% Death Save	0% Bonus Profits	0% Bonus XP
Enemies	at 140%	Challenge 130%	No combat boost