FirstLight is not thinking through the situation. FirstLight is their ISP, and delivering the dial tone via an IAD, or router with FXS ports. Yes, it is SIP from FirstLight's servers to the premise, but it is ANALOG DIAL TONE from the handoff to the PBX.
Nothing the customer can do, FirstLight's "tech" needs to come on site with a butt set that displays CID and can break down the the messages, working with their internal support and possibly the router manufacturer to resolve.
Again, the information that they are sending for Caller ID between the 1st and 2nd rings includes the Month, Date, Hour, and Minute, and then either a flag to indicate Unavailable (number was not sent from originating CO), a flag to indicate Private (caller has CID Blocking on their line or has dialed *67 before placing the call), or the 10 digit telephone number. Proof would be to set the time correctly on the Partner, place a call from your cell, and observe the clock changing just after the first incoming ring is received.