At small sizes (<= 16 ppem) some Cyrillic in Serif are rendered with issues due to instructions:
1. Breve in Й, й, Ў, ў is not centered.
2. Middle horizontal stem in в, з may be rendered below the middle. The upper arc must not exceed the lower one.
3. The arcs in я, љ, њ may be too small in vertical direction.
4. The skewed stems in м, ж, к are too bold when compared with "v", "w", especially м. The same with ascender in б.
5. The joining stem in ю should be at center or higher.
Look at screenshot made for 14 ppem.
Created attachment 10623 [details]