There have been several threads about using DMX741 to receive C & Ku on dishes mainly 6 ft and larger. The problem is when you get C band aligned the Ku degrades and vice versa. I use this lnb on my 6 Ft Fortec Star Polar mount and have encountered the same issues.
There are very few members(2-3) that have success getting both C & Ku to have maximum peak signals.
With that be said, if there are issues with larger dishes (6ft and higher), the problem will be more pronounced using a smaller dish (120cm/4 ft). It is a great lnb, but I decided to have a separate C band dish on an actuator and a 120cm using a H2H motor.
You might get some very strong C & Ku, but the signal will be weak, and weak signals will not be received. Normally it would be best to peak the Ku first and then check the C band.