Placement of Icons?

I am thinking of the festal icon, in particular -- should these be before the iconostasis (as in the Slavic churches) or in the vestibule/narthex (as in the Greek churches)? And how is the procession of the festal icon be affected by the difference in location? If we accept that it is the entrance into the temple itself by all of the faithful that is of importance, rather than the entrance of the clergy into the sanctuary, that matters, then it seems that the festal icon should be located in the narthex. (That is to say the "holy space" is the temple proper, and not the area surrounding the altar, the "sanctuary."

Then is it appropriate to have another set of icons of our Lord and the Theotokos in the narthex as well? Should the narthex be the only locus of the veneration of icons? I don't think that necessarily follows from what has been said about placing the festal icon at the entrance to the holy space, i.e. the "nave" of the temple. But that does seem to be the standard Greek practice. Is it possible to have a mix of the two customs?