I have seen several FOs on reserve in DAY that are not based in DAY. The contract doesn't specifically address TDY reserve. (at least I couldn't find it) which I take to mean that TDY reserve is not allowed.

The only reference that kind of addresses it, is

12.B.3

"Rest in domicile between reserve (availability) periods will be scheduled for a minimum of ten (10) hours between reserve periods and in no case will actual rest be less than nine (9) hours."

meaning that if they do want to DH you for reserve then they have to get you back to your domicile between reserve periods, and you cannot sit hot because any layover greater than 4:45 requires a hotel

Anyone who has been subject to this needs to contact the CP and the union, this is a breach of contract. If the company wants pilots to sit TDY reserve then they need to draft an Letter Of Agreement that outlines the specific rules and compensation.