Hi,
True. The reason for that is the reported distance of an EIGRP route has to be less than the FD of that route to become a feasible distance/successor.
A simple example would make it easy to understand.
NETA----RouterA-----RouterB------RouterC
RouterB- FD to NETA is 60 via RouterA
RouterC- FD to NETA is 70 via RouterB
Based on the above EIGRP rule RouterB would consider RouterC as the feasible successor only if the route to NETA advertised by RouterC is less than 60. If infact RouterC's reported distance to NETA is 60 or less then RouterB wouldn't be feasible successor to RouterC for this network at all.
Thus two adjacent routers CANNOT be feasible successors for each other for the same route.
Hope that makes sense and helps!
Regards,
Sundar
