An incentive to move can only be paid if the evaluation of staff under a formal performance appraiser or evaluation system is at least “fully successful” or equivalent. An agency may also find that a position is likely to be difficult to fill if the Agency is likely experiencing difficulties in recruiting candidates with the skills (i.e., knowledge, skills, abilities, behaviours, and other characteristics) necessary for the position (or group of positions) if there is no incentive to move based on the factors listed in 5 CFR 575.206(b). An agency may also find that a position is likely difficult to fill if OPM has authorized the use of a direct tuning authority for the position. Basis for the finding that the worker is likely to leave the federal service if the incentive is not granted The worker`s required length of service may not exceed four years. . . .