I sort of alluded to this in the comments but I think this is a topic that needs a lot of semantic brush-clearing before one can really get the lay of the land. Lacking that, though, my intuitive feeling is that this distinction is really about the sociological/pragmatic dimension, whereby "ethics" is related to this idea of an intangible reward alloted from somewhere external for actions which we like, but which are otherwise poorly remunerated.
Like if you think about art or charity or other good works, there's a sense in which it's "more ethical" if it's harder and less directly remunerated, for a constant quality of output. I'm not sure if this extends to cases where you're just deliberately focusing on things that you're uniquely bad at, but in general, all else equal, "ethicality" goes up with sacrifice and hardship even in the context of personal excellence. It's more controversial, but people often round this off to attributing virtue to hardship and sacrifice in themselves, without regard for outcomes!
It seems to me that relative to the most abstract "good", "ethics" implies a kind of exterior incentive structure, to the point where converting one's moral instincts into an ethical framework requires some explicit mechanism for exteriorizing it, like the categorical imperative or the will of God. And the kind of external incentives that yield ethics have to be in some sense deliberate; weather and topology can't be ethical constraints in and of themselves unless you anthropomorphize them as divine intention. So this is where "the good" comes into it, I think -- if we're talking about deliberately constructed incentives then there has to be some logic guiding their design, and so "the good" enters into it there, but there's a further narrowing constraint at work, which is the degree to which these added moral incentives seem productive of the desired result. And I think this is where max's comment about the deontic element comes into it.
A normative framework of "you should produce great works of art" isn't very useful, because it doesn't help with any of the constraints on the production of great art! Similarly, improving your personal health and strength is more "virtuous" than "ethical" because it is its own reward; an ethics of personal excellence mainly emerges in cases where the benefits are remote and uncertain ("sometimes there is a luxurious amount of time before anything bad happens") or where the costs mostly accrue to the individual and the benefits mostly accrue to society (e.g. diligent work in the underclass). "Ethics" has more of this sense that the acts in question are good but nonetheless also require a kind of extrinsic moral subsidy in order to be worth doing, and the degree of ethicality is a combination of the marginal goodness of the thing we want to incentivize and its perceived responsiveness to this subsidy. This would make it closely related to blame, merit, choice, and law, all of which are pragmatic social technologies at their root.
Of course, there are complicated relationships between all these things. Normally we don't like to attribute an ethical character to things outside someone's control, for instance, but it still happens all the time, either because we misjudge their level of control, or because we're coping with our anxieties about surd evil by attributing it to misdeeds that we trust ourselves not to commit. But these are all just results of adding extraneous sources of error to the original mechanism.
This explanation seems unsatisfying in the sense that it's pragmatically mechanical, but you need some subjectivity to explain how variably ethics are construed. If this seems too subjective, "the good" is still out there in all abstraction deciding what you want, and the specifics about its responsiveness to incentives are simply "the truth". But there is no single answer to the latter question for all times and places, for the same reason there's no single answer to "how cold is it"; the objectivity is in the destination and in the general logic you follow to reach it, not in the path taken.
