you also should check what buffs enemy uses to increase reflect because if tank has 150% reflect or something, your longing wont help yo much because only it wont give to much reflect rezistance
reflect resistance works as an additive % of amount reflected onto you. for example:
Longing is reflect resistance 30
if Tank reflects 1000 dmg, you will receive 700 dmg
Also, somewhat of an interesting point, there is no point to have more than 100 reflect resistance. If a tank has 150% reflect (which is possible), and you hit for 1000 and are getting 1500 reflected back to you. Having 100 reflect resistance would null the reflected value to 0, regardless if the tank is above 100% reflect. 100 reflect resistance would negate all reflected damage irrelevant of amount reflected.
in testing longing reflect myself this morning, it appears to be working as i described above. not sure what you are doing or looking at.