To zephyrblade: The attack player name or id in the war room should be cleared if you want to go to the enocunter. If it's not cleared, and it has a number, the attack will go to the player instead. I will make a patch to this, so it will clear automatically.
The cost calculator for missions and encounters takes into account your fleets cost*2.5, that's 2.5 x fleet costs as base, so yeah, the fleets you encounter should no more than 2.5 your fleets cost.
E.g.: To experiment, make some I Shuttles, get everything else into reserve. Then, try an encounter. You will notice you meet no oposition, or a very small one. The reward will be adjusted in that case, so you won't get much of a reward using this tactic... (close to a glitch actually)
Encounters should not be done if you have a small % of your power in fleet power, e.g. you have 20 mil power (15 mil resources and 5 mil fleets), and try to complete a 20 mil encounter. Odds are against you then, your 5 mil fleets will go against 20 mil fleets, that can have 2.5 your total fleets cost...
My sugesstion is to control the encounter fleets you meet by controling your total fleets, and also try to have more fleet power than resource power, that will surely happen in the future, since comanders start at a 90% to 10% ratio on resource -> fleets, and end up at a 10% -> 90% ratio in some time.
Basically, at this rate, and with some commander bonuses, encounters will start to be more and more profitable, and affordable, but they are a little hard now, but don't be discouraged, the ballance will turn in your favour soon
God Speed!