I never thought of weight under the ESC, must see if I can get a brass plate or something made up, that may be good.
Got to look at the Reflex fan mount, if only because it adds weight in the right spot, I came super close to failing a weight check today, was 4g over min limit, had a tyre blow out (and then followed by the motor), got loaned a spare motor (same as my own), but also tried some different tyres in a final run, only to walk off the drivers stand and remember I'd just changed tyres, and not re-checked the weight, got super lucky and came in 1g over legal weight.