Just tried your modification! As you said: works great for the ground and similar angles (tried it also with a prefab sphere), but not at the walls(and their vertical angles)!

Does anybody have an idea how to solve this?

BTW:
//works for ground and similar angles:
Out.View1.x = vecViewDir.x*-1;
Out.View1.y = vecViewDir.z; //(!)
Out.View1.z = vecViewDir.y; //(!)

//works for walls in y-direction and NO(!) other angle:
Out.View1.x = vecViewDir.x*-1;
Out.View1.y = vecViewDir.y;
Out.View1.z = vecViewDir.z;