Cannikin:
Tight? Just that.
The Frontier contract with Horizon calls for a fleet of 9 CR7's and up to 20 - if Frontier wants that many.
In order to supply the original 9, Horizon had to pull some CR7's from it's own routes - and even now, I believe that 1 of the 9 Frontier Jet Express aircraft will also sub for Horizon flights - or it did.
Horizon has a few more CR7's on order but not enough to let both Horizon and Frontier Jet Express expand.
So - Horizon could probably use some more aircraft for itself, and certainly if Frontier wants to expand Jet Express, then Horizon would have to find some more aircraft.
In which case, the EMB170 might make a lot of sense. If Horizon wanted to keep it for their own flights, it might free up some CR7's for Frontier.
OR - because Horizon gets paid all costs plus a profit margin by Frontier - a couple of them in the Jet Express fleet would be making money (for Horizon) from Day 1.
cheers
mariner