The guy in that You Tube video is not putting it on correctly in my opinion - it's for the camera and the most important images are him and the bathroom. The advertising agency are using his image to sell the product.
I changed to foam in August last year and I've been persevering with different methods of application. My hair is 3-4 inches long and for the first few months I applied it directly onto the head by placing the nozzle on the scalp in several places, then patted it down and lightly rubbed it in.
More recently I've put some foam in my hand and immediately pressed it into the front hairline, tipped my head back and rubbed it vigorously into the scalp working from the hairline towards the back of my head (I only have frontal thinning and take propecia to maintain the crown area.
I feel that this vigorous rubbing has been giving better results, so I'd go for that. What you must remember is that the minoxidil must be absorbed into the scalp - that's not a problem with the liquid, but if you don't get the foam directly to the scalp it will sit on the hair and not be absorbed, so I believe that by vigorous rubbing you're really getting maximum absorption.
A can lasts me just over three weeks using this method.