I'm looking at a number of extended Cyrillic diacritic letters,
i.e. characters used for non-Slavic languages, and am wondering about the appropriate/preferred style of the breve mark in these glyphs. The characters in question are
04C1 Ӂ CYRILLIC CAPITAL LETTER ZHE WITH BREVE
04C2 ӂ CYRILLIC SMALL LETTER ZHE WITH BREVE
04D0 Ӑ CYRILLIC CAPITAL LETTER A WITH BREVE
04D1 ӑ CYRILLIC SMALL LETTER A WITH BREVE
04D6 Ӗ CYRILLIC CAPITAL LETTER IE WITH BREVE
04D7 ӗ CYRILLIC SMALL LETTER IE WITH BREVE
The form of breve sign used for the Slavic characters
0419 Й CYRILLIC CAPITAL LETTER SHORT I
0439 й CYRILLIC SMALL LETTER SHORT I
040E Ў CYRILLIC CAPITAL LETTER SHORT U
045E ў CYRILLIC SMALL LETTER SHORT U
is conventionally larger than the Latin breve, and stylistically quite different in serif types. I am wondering whether it is appropriate to carry this convention across the extended Cyrillic diacritic characters, i.e. to have a single Cyrillic-specific breve form, or if any of the language communities using these characters have a preference for a breve that follows the Latin model? Anyone have any information?
Fig. Typical stylistic difference between Latin (left) and Cyrillic (right) breve forms in serif type:

Comments
https://loc.gov/catdir/cpso/romanization/nonslav.pdf gives О̆ о̆, Ы̆ ы̆, Э̆ э̆ in Mordvin (Moksha dialect) in the 1923 orthography, but no Ы̆ ы̆ in Mari.
http://www.helsinki.fi/~tasalmin/TN-suomi_2011.pdf gives a few used in Tundra Nenets: Ӑ ӑ, Я̆ я̆ but this might be specific to some usage since https://en.wikipedia.org/wiki/Tundra_Nenets_language mentions a different set: Ӑ ӑ, Ӗ ӗ.
There’s also Ҋ ҋ in Kildin Sami.
Even if someone writes /ka-cy U+0306 or /yu-cy U+0306, your font should sub the form of this combinig breve to the Cyrillic one.
In practice this might be different, for example in the Tundra Nenets document I referred to earlier http://www.helsinki.fi/~tasalmin/TN-suomi_2011.pdf where the Ӑ and Я̆ don’t have a kratka-shape. I think I’ve also seen phonetic transcriptions in an extended Cyrillic where the breve-shape is used. But I don’t know if either is on purpose.
See for references free ParaType fonts PT Sans and PT Serif - special designed (government order!) for cyrillic based alphabets in Russia.