I had a similar problem and added the support to the docx library.
The forked docx code is in https://github.com/Oritk/python-docx
Usage:
run = p.add_run(line)
#ru.font.size = Pt(8) ### This line is redundant - but you can leave it
run.font.cs_size = Pt(8)
run.font.rtl = True