Problem visualizing and printing thin font



I'm designing a font family of nine weights and when I try it on MS Word here comes the problem. I know MS Word isn't the best typographic program but there are some people that use it and deserve quality on fonts.
The problem happen only in the thinnest style and consist in the following:

As you can see in small sizes the MS Word expand the character shapes and the real proportions aren't showed.

If anybody can help me I apreciate it very much.

Thank you in advance,