Other Insurance and Personal Property at Secondary Residence

Our insured had a total fire at his vacation home. The home is insured on a DP 00 01 (07 88) and includes a limit of $5,000 for contents. There was no problem with settling the loss for the building, but now we are questioning the adjuster's offer on the contents. He wants to see the insured's primary homeowners policy in order to apportion the contents settlement. He says that since the primary homeowners policy probably provides 10% off premises coverage for property at another residence, it should contribute. Consequently, the insurer has offered a reduced settlement based on what it thinks its portion should be.

The insured's primary homeowners is insured on an HO 00 03 with another carrier. Does the policy language regarding personal property usually located at an insured's residence, other than the residence premises, bear on the vacation home insurer's right to apportion the claim?