I agree with letting your stirrups out just a tad. Just enough to let your fenders hang straight down and that will also help get that big arch out of your lower back so you can move a little free-er(sp?) through your lower back and hips.
What you are doing will determine your stirrup length some. I change mine between all day riding(longer) or corral work, colt starting or training.(maybe a hole or two shorter) I actually like that your stirrups were a tad short rather than too long. Some think that riding western=long stirrups. I see that they stand on their toes and shove themselves against the cantle to stay in the saddle and in turn makes for a hard hand.
Personally I think your English background makes for a great base for riding western!
Good job and I am glad you made it to the states to see Sky!(or maybe you had him shipped NZ???)
I wish I had him shipped to NZ! I was definitely in the states for too short a time.. will aim to spend more time there next go around! At least I got a little try at western :)