If you can't adjust the fan speed, you could always try to put some kind of shelter round the sides of your tray to keep the draft out. I'm not sure how that would affect the baking times, though.
Here's a few threads about the problem, if you want to sort through the advice.
http://cakecentral.com/t/733438/i-need-help-quick-lopsided-cupcakes-in-commercial-oven
http://cakecentral.com/t/716655/fan-assisted-oven-night-mare-plzzzzz-help-me
http://cakecentral.com/t/737211/i-thought-convection-ovens-were-supposed-to-take-less-time
Quote by @%username% on %date%
%body%