Unable to reduce size of subtitles with VirtualDub

I have a German speaking avi file of about 1.73 GB(when I checked with AVIcodec what's the codec of the said file, AVIcodec showed "unknown").
After downloading Czech srt subtitles to the said file I used VirtualDub (version 1.8.6) to "embed" the said subtitles into the avi file. In the TextSub settings > styles I choosed "EASTEUROPE" (instead of DEFAULT) and Arial font size 24. Next, after compressing the said avi file with DivX 6.8.5 Codec (2 Logical CPUs), I selected "Saved as Avi".
During the process of "embeding" the subtitles the fonts seemed to me be too large, however I didn't stop the process. Only when, after watching the movie with a standalone DVD player, I saw that the subtitles are really too large (and some sentenceappeared in 3 lines). Hence I repeated the whole process with VirtualDub, only that this time I choosed the same fonts (Ariel) size 22. To my surprise, the size of the subtitles were as big as before (whe I selected 24). Moreover, even when I selected size 18 the subtitles were as big as before.
I should add that I used VirtualDub many times and I never encountered such problem.
Hope somebody there will be able to help me to solve it.
Thanks in advance
stibi