This is my trick to fit chibi models to motions, so they won't dance with their feet too far apart. An example:
1. Changed the size of Pxchm-Neru to 109% with PMX-editor, so she became equally tall as Animasa-Miku
2. Changed the size of the x-file stage to 109% in this red marked square, so to model-to-stage size ratio looked unchanged
That is a good idea. Chibi models always give me trouble.