Can't invite a 3rd master.

I've reached level 6 with both Haku and Elreon but I still have no option to invite an additional Master to my hideout.
I dismissed Haku after he reached level 6 (he was first) and invited Elreon but it still won't allow me to Invite another.
The other Masters all say my hideout is full and I need to dismiss one to invite another.

I might have misunderstood something but from all I've read getting a master to level 6 should be enough to be able to invite a 3rd one.

Having a Level 6 Master unlocks the bigger hideout from him. Only if you have this bigger one you can invite three masters. Simply having a Lv6 master will not be sufficient.

Thanks a lot, never would've figured this out I fear, thanks a lot for the quick response.