Heh, awesome. much better than just black to a white background.
However I regret to tell you I've found a flag possibly better suited for Afghanistan ^^;
The Durrani Empire wich is the first actual Afghan state. It was Established in Afghanistan 1747 and separated from the Persian Empire.
this was their flag:
And this is their coat of arms wich has been kept in Afghanistan until this day. It could be used as inspiration for a battle flag:
Sorry I didn't realise about this sooner, the Pasthuns caligraphy is still a very nice alternative though.