As you an see, on a Birdy with front light, the stopper plug is mounted on the front light adapter plate. This one can be adjusted .

Maybe this plate is not placed the same on your bike as on my bike?

On Birdy without front light, the stopper plug is directly bolted in the fork and its possible to do so on a Birdy with front light by mounting it on the left side of the fork that has the same threaded hole than on the right side (hole which is used to mount the front light adapter plate).