If you didn’t get round to bolting it up you wont know

the bracket sits on the rubber after the washer so it's just like a washer, then drops down but is not hard up to the cooler, couple of mill gap, this is why there is a little flex, if forced with the hand backward, depending on the weight at the front of the bracket it just sits there when the engine is on, as any vibration is absorbed into the rubber and then if the cables are tied back stops bracket movement.
Yes if you then get hold and force it back it would move, but under normal use it sits and does not move or vibrate.
The ones I have fitted have little (only the heavier ballasts) or no movement.
Best to mount the ballasts, fit the bracket then tie the cables back to each side then see how it all looks, after that if you are still not happy then tryfastening it at the front with tie wraps or then a bolt.
All the ADV’s that I have done with and with out spotlights have been the easiest to fit as the shape of the bracket sites well with the engine bars, there does look a little more space if the spot light bar is no fitted but mount the ballasts to the top side of the bracket and you can hardly notice them.