Speaking not as any official representative, but as a colleague of Derek's and someone that's sung for him for quite some time, I wouldn't say it's "chironomy" per se, which would indicate a particular way of thinking of the chant (that is, something specific even in a larger division of "chant conducting"). I don't think that's what Derek is going for. He just has a particular way he wants things on air.
It works for what he does; in a very different way, we have a blended approach at the Cathedral in Birmingham. There would be a lot of pitfalls and unmusicality in what we do if we slavishly adhered to "old Solesmes", in my opinion, just as there would be if we took a more radically semiologically rooted performance style. So, I try to take the best from the various approaches, also considering the tastes of the clergy and people (and the strengths of my singers).
I know this probably clarifies nothing! But, I think it's accurate all the same.
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