Nat,
* Is there such a tradition?
It is possible to do that kind of operations when setting the palt data for 「。」, i. e. shifting the glyph image of the punctuation leftward virtually by using the palt mechanism with the virtual total escapement width of the type body unchanged. I believe there are fonts using this technique in the palt data setting. However, as the method affects the left-side space of the punctuation, it depends on the boldness, the shape of the punctuation and/or the main usage of the font whether it can be used or not, I guess. But as far as the ‘palt’ feature (and probably the ‘kern’ feature also) need to be applied, I doubt it can be said that this method works for the em-based grid, though there may be cases where this is effective.
Just my thought.
Best,
--Taro