some of these cheaper LNBs ,universal, have an arrow on the throat with a couple of notches on either side of it.
Does this mean you have to turn the LNB a certain way?? even if its a uniform round throat..
However I would add that I would take the "recommended dish size" as just that, a recommendation. It is usually overly optimistic for C-Band, as well as for marginal Ku-Band signals, and I think it's only based on EIRP, and does not take into accounts other important factors such as modulation (8PSK requires a stronger, cleaner signal than QPSK), FEC (the higher the FEC, the least robust the correction is, thus requiring a larger dish for a cleaner signal), the actual transmitting power of the uplink, the beamwidth of a smaller dish (interference from adjacent satellites) and the elevation (only a problem at low elevation).
Example, 103W, where the transponder with NHK is easy even on a 50cm dish, but some of the NBC transponders can be quite challenging even on a 120cm. Or BVN on 113W where for my location, an 80cm dish is the recommendation. Well, with 80cm you barely get it and there's little to no margin for any degradation due to weather etc.