While the ratings aren't 'horrible', they are showing a steady sign of dropping fast.
The best chance this show has is FX being very understanding.
FX allowed It's Always Sunny in Philadelphia to grow into one of the channel's biggest hits, the first season of that series had pretty bad ratings, but the channel trusted the word of mouth to increase its ratings and renewed it.
The League had pretty mediocre ratings too, but got renewed for a 13 episode second season as well.
The only difference is The League posted some increases in ratings, however small they may have been. I don't know how easy FX will be on Archer if the show continues to drop, we better pray it increases in some way, justifying FX to renew it.
FX promoted the hell out of Archer, I think the show's main problem is it has no solid lead-in series and it's airing at a very bad timeslot where it is competing against all the most popular shows on the Thursday night 10 PM timeslot. FX should really split It's Always Sunny's seasons up into two different chunks similar to what Comedy Central used to do with Reno 911 and now do with South Park. This way, it could have benefited Archer to have Sunny as a lead in.
FX is a pretty laid back channel and is similar to HBO in the sense that when a series gets good buzz, they tend to allow it time to grow, rather than just cancel it with trigger fingers like Network TV channels. So, we can only hope they give this show room to grow.