There is another variation that allows ruby text to overhang any
ideographic characters (cl-19), hiragana (cl-15) or katakana (cl-16)
up to the full-width size of a ruby character (see [Fig.137]).
but it seems to me that the ruby in Fig. 137 overhangs adjacent
ideographic and kana characters by half the size of a ruby character.
In particular, both instances of "ふところ" ruby has forced extra space
around the "懐" base characters.