There are many things that need to be considered. System coveraged / bridging options. The phone programming (call appr, restrict last appr, etc), the cover path programming, the presense of bridged appearances on stations that are cover points, the state of the primary station when called and it's call appearances.
Possibly the state of the cover points.
You should read Avaya Feature Docs on Call Coverage, programming, interactions, considerations, limitations.
This is a very flexible feature and you have not really provided enough information for a good answer.
A great teacher, does not provide answers, but methods to teach others "How and where to find the answers"
bsh
35 years Bell, AT&T, Lucent, Avaya
Tier 3 for 25 years and counting