User blog comment:Omega natsu2/Fairy Tail Episode 213: Erza vs. Sagittarius: Horseback Showdown!, Review./@comment-2125188-20141220113248/@comment-2125188-20141220114842

First of all, it's not 2 spirits every episode. So far it's been 9 spirits in 6 episodes, so about 1.5 per episode. Also, I personally belive fights involving Leo, Virgo and Ophiuchus in particular are the more important fights in this arc and will take about 1 episode each (or possibly more).

2 episodes for 4 spirits and to wrap this arc seems unlikely to me.