The dish is made of around 1mm thin metal and it warps when you mount the support brackets at the back, you can see this in any 2nd generation T90 where the bolts goes thru the dish, i would say the 2 bolts in the middle as there are 6 bolts to the dish.
It is fixable if you have some know-how, i did reconstruct the brackets so no warpage occured by extending the distance between the brackets to the reflector at the upper part of the dish, eg the two upper holes of the dish.