Hi zox
On the school i attended in Norway, we had a few instructors who were about your size.
Granted, it made planning a bit harder, and some of the longer navtrips we had to shorten down, but for circuit and near-airport flights (which constitute maybe 90% of the dual flights) it made no difference.
Be aware however, that the R22's have slightly different dryweights and moments, some will make absolutely no problems for you, while others (often those fitted with a lot of instruments) will make problems for even the skinniest FI's
If you want to check, try filling out a weight and balance sheet for a robinson 22, you can find them all over the web, and see what happens. -Just remember that most calculators use pounds
Fly safe!