Given that most possibilities have been discussed, then perhaps it's the paint itself.
Did you give the paint a good stir before mixing with thinner, and then ensuring the thinner/paint was fully mixed in ?
Matt black enamel, in particular, always needs a thorough stir before use, to ensure all of the pigment is dissolved into the carrier. As previously mentioned, there were definite quality problems with Humbrol enamels a few years ago, with some colours being particularly bad, including black, red, blue and some of the greens. Since a change of manufacturing source, this now seems to have been sorted, although a few colours are now different totally to what they once were, with Number 11 Silver, for example, now being dull and "speckled" in appearance.
I would suggest obtaining a new tin, stir thoroughly, thin to around 40/60 thinner to paint and test this in the mixing jar by allowing it to flow down the jar with the consistency of milk. If it doesn't, then sparingly add thinner, drop by. drop, testing between each addition until the desired consistency is achieved.
Once satisfied, test spray at around 15 psi, from between one to three inches, varying the distance until a satisfactory spraying range is achieved.
Although it's tricky to ascertain from the photos, to me the results so far suggest over-thinning and spraying from too far from the subject.
Hope this helps.