like I said, the coordinates aren't the problem here, it's rather that the decal covers two meshes, Left/Right_VStab and Left/Right_rudder. (I do think that the meshnames are correct.)
[Decal005]
MeshName=Right_Vstab
DecalLevel=3
DecalFacing=RIGHT
FilenameFormat=SU-27N/Grey Camo/D/LT
Position=-5.9,2.2
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal006]
MeshName=Left_Vstab
DecalLevel=3
DecalFacing=LEFT
FilenameFormat=SU-27N/Grey Camo/D/RT
Position=-5.9,2.2
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal007]
MeshName=Right_Vstab
DecalLevel=2
DecalFacing=RIGHT
FilenameFormat=SU-27N/Grey Camo/D/RTailnum
Position=-5.8,1.7
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal008]
MeshName=Left_Vstab
DecalLevel=2
DecalFacing=LEFT
FilenameFormat=SU-27N/Grey Camo/D/LTailnum
Position=-5.8,1.7
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal009]
MeshName=Right_Rudder
DecalLevel=3
DecalFacing=RIGHT
FilenameFormat=SU-27N/Grey Camo/D/LT
Position=-5.9,2.2
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal010]
MeshName=Left_Rudder
DecalLevel=3
DecalFacing=LEFT
FilenameFormat=SU-27N/Grey Camo/D/RT
Position=-5.9,2.2
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal011]
MeshName=Right_Rudder
DecalLevel=2
DecalFacing=RIGHT
FilenameFormat=SU-27N/Grey Camo/D/RTailnum
Position=-5.8,1.7
Rotation=0.0
Scale=3.0
DecalMaxLOD=3
[Decal012]
MeshName=Left_Rudder
DecalLevel=2
DecalFacing=LEFT
FilenameFormat=SU-27N/Grey Camo/D/LTailnum
Position=-5.8,1.7
Rotation=0.0
Scale=3.0
DecalMaxLOD=3