Hi SATCO, I did a search on Google but that did not come up with an explanation. I assume the Russians had a good reason for their design.
Leaving asside the issue of the AH, I found the Yak9 a great aircraft to fly.
I note your association with Biggin which, for me , brings back very happy memories. In the mid 80's I flew my Beech Bonanza from Melbourne, Australia to the UK and landed at Biggin Hill. The Bonanza is no longer part of my life I now potter around in a Chipmunk.