Weight isnt a matter, its all technique! the only people that will notice that the weight is a help is people that have been in the game for ages! people who start on a light bike wont be able to manual straight away because its light..
rant over.
And yeah, back to the question, i found leaning you bum over the rear end that it was inline with the axle helps, it doesnt matter if your front wheel is two feet high or two inches, aslong as your front wheel is up and your keeping the bike under control it doesnt matter.. manuals take hours and hours of practice! good luck!