Concur with all of the above. An additional consideration is if you are only going to put two missiles on a quad HML (Hellfire Missile Launcher) side-by-side is preferred to over-and-under. For the Cobra, what is being carried on the inbound store will also affect how many you can carry and where you should put them. Too many variables for me to cover all the possible options. If you have a speficic load or aircraft you want to model let us know and perhaps someone here can tell you if it is legit and legal.
Also, with the pictures you can never tell whether they are coming or going so a picture of less then a full load or one station loaded rather than another may be because they expended something and brought the others home. There is a set firing order for the launchers but you can override that and now that we are carrying up to three different types of HF missiles on the same station you may see one selected and fired from other than the automatic sequence.