I'm not sure I understand your question.
For teeth to mesh they must have pretty much the same spacing (teeth per inch) on each gear (sun,planet,ring) and so the radii of the gears are in proportion to their number of teeth.
Since the teeth interleave the question arises to what you take as the radius: the internal radius (innermost cut), external (furthest metal), or 'somewhere between' makes more sense, but precisely where?
A planet gear will be half way between the edges of the sun and ring gears.
The rest will be spread out most sensibly opposite each other (if there are 2), in an equilateral triangle (if 3),in a square (if 4) etc.
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Are you expecting a detailed answer dependent on tooth profiles, tooth gaps,etc?