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An ad-hoc network using unmanned aerial vehicle (UAV) as relay, has been gaining significant attention especially for communication between far apart ground terminals during emergency conditions due to agility and resilience requirements. However, UAV hovering localization (HL) and power allocation (PA) are the key issues in such relay based flying ad hoc networks (FANETs). In this work, we propose a framework to jointly optimize the placement of rotary-wing UAV hovering and PA for maximization of network throughput in a three node decode-and-forward (DF) FANET. Specifically, we develop three different optimization schemes, (i) individual UAV HL optimization with a fixed allocated power, (ii) individual PA optimization for a fixed UAV HL, (iii) jointly optimal UAV HL and PA. For every optimization problem, the underlying convexity is proved and the global optimal solutions have been obtained. Further, we provide novel analysis by utilizing the characteristics of sigmoidal function thereby obtaining the closed-form and semi-closed-form expressions respectively for the globally-optimal solutions for individual and joint optimization schemes. The analytical results are numerically validated and various optimal design insights are discussed. It has been found that the proposed joint optimal scheme shows an average performance enhancement of 52% over benchmark scheme.