The problem doesn't come from your bar or the length of your arms. If I look back at the graphs from your area on the week-end it seems you didn't get much more than 20 knots, is that correct?
Assuming you don't weight 50kg or less you definitely shouldn't be overpowered in 20 knots on a 10.5m kite, in other words you shouldn't be riding super fast and out of control with your bar sheeted out.
So my conclusion is that if you weigh 70kg or more and were overpowered on a 10.5m kite in 20 knots, is that your lines are out of tune. Over time your center lines stretch and become longer than the back lines, this means that you have to hold the bar further away than usual and you lose the ability to depower the kite.
The video below will help you to understand how to tune your lines, even if it's for a cabrinha bar the same principle applies for any other bars on the market. If in doubt ask and experienced kiter to help you or go to your local kite shop for help.
Hope this solves your problem