You're right that Cambridge is a more spread-out area than others, but I looked up the Priceline hotels in the zone, and in my opinion only one would be significantly more annoying to access via the MBTA than the Copley Square zone that was chosen by the OP. That's the Doubletree which would require a moderate walk across the river to the Green Line, or a bus to the Red Line. The others are all within a few blocks of the T. The Meridian, Sonesta, Marriott, and Residence/Cambridge are all on the Red Line, thus easier to reach for a Convention Center trip. The Marlowe, Holiday Inn Express, Courtyard, and Hyatt Regency are on the Green Line, offering a similar 2 transfer ride as Copley. The Residence/Boston Harbor is also a little tricky but within walking distance of 3 subway lines so it's also fairly convenient. So, if saving money is a top priority and opening another zone in Priceline would help, I'd still recommend including Cambridge in the bidding.