What you are describing is the reverse of the usual pattern, which is the part worth attention. In typical male pattern loss, the sides and back are the resistant zone, the areas that hold while the top thins, and the regions a transplant draws from precisely because they stay stable. So, sides thinning while the top stays dense is the opposite of the textbook picture.
Two things to separate. The hair over the ears is naturally the finest and lowest in density and looks worse than it is under a close flash, so some of this may be lighting. But if the sides are genuinely thinning and progressing, that is the part to take seriously, because loss in the normally stable zone points away from standard pattern loss and towards either a non-androgenetic cause or a diffuse, unpatterned type. Those need a real diagnosis, not an assumption, because the cause determines what you would do about it.
I would have it looked at properly, ideally by someone who can put a scope on the scalp and read the miniaturization, before treating it as ordinary loss. The top holding that well is a good sign. The sides are the area I would want examined first.