Dr. Kashif Ameer has mentioned about the optimum concentration of calcium lactate as 1.25percent. He has also provided a reference material to support the suggested value.
You can refer to standard tables/graphical representation of percent concentration of calcium lactate and the corresponding water activities of such solutions.
You can safely choose that concentration of it which matches to the corresponding water activities of meat under consideration.
Original moisture content of meat, whether it is fresh or processed, whether it is lean meat or is it reach in fat content, whether you are going to add any preservatives and antimicrobial compounds such nitrates and nitrites whether it has given any smoking treatment or not etc. has to be considered while choosing the most appropriate concentration of calcium lactate to get best results.