Adjustment of a composite front door assembly?

I had a nice, substantial front door fitted around 3 years ago, but now the door has dropped slightly, meaning that the lock tang will not engage in the slot, so that it has to be continually locked. The top hinge assy certainly looks as if it has dropped slightly, but there does not appear to be any way of lifting the hinge cover to reveal any adjusting screws. . . .I'm wondering if the vertical hinge pin is designed to be eccentric so that it can perhaps be adjusted from the top ? ? I don't want to risk damaging the assembly and have had no success getting any local tradesman to come and have a look ! !