As Tiger Shark rightly put it, I am now leaning on placing the main IDS just inside the main firewall and placing some more secondary sensors inside of the network to monitor the intranet traffic. I am gonna have to do this in all the locations on the network. Yes it is gonna be a multiple collision domain. Thats why I in consultation of my colleagues have decided as you rightly put it, to place some sort of secondary sensors for the internal traffic and the traffic between our various locations.
The deployment might start off sometime next week hopefully(keeping fingers crossed).