Almost certainly CofG requirements as the primary consideration.
Not an expert in the Tiger...but weren't the wings altered in config when it became the defaco RAF trainer to give the forward seat a better view and/or better escape egress possibility in the event of a bale out being necessary......
As I recall the centre portion of the wing was moved forward on the fuselage thus giving the a/c a swept back wing config. This in turn would have required some dihedral to be introduced to maintain stability. I think the upper and lower wings have different dihedrals.
All this would certainly have changed the CoG calcs on the a/c.
Regards