Resource Detail Site Assignment

We are struggling with assigning users under “Assign Work” from the Prepare Work Order screen, under the “Allocate To” for users who perform work at multiple sites. We have the users set up in the Resource Detail with Companies and Sites assigned to them under the Connections tab. We also have their site assigned under the General tab. However, when we need a user to perform work at a site other than what is listed as their Site under the General tab, they are unavailable to be chosen under the LOV “Allocate To”. Has anyone else found a way around this other than changing the Site under the Resource Detail → General tab each time a user needs to perform work at another site? We are running APP10.