,
Thats because the Slimline is big.
Try Using a Phase III dish with a Slimline 3 LNB. And you will see what we mean. It not reliable at all in weather.
Remember 99,101,103 is a smaller space to cover then the 101,110,and 119 that the Phase III covers with no problem.

the 1000.2 and 4 are only 19x24 but cover much grater span between satellite locations
D* needs a 24x32 dish because of the narrow band that KA puts out.