the sequence of rounds shown is correct and this is the ONLY sequence that works properly. It works fine for ANY .303 rifle, including SMLE, Number 4 and 5, P-'14 and Ross.
Pressing the thumb as close as possible to the base of the rounds definitely improves feeding.
If you have a Dremel tool, you can slick up the insides of the feed lips of many clips (there are a lot of bad ones; they were made to be used once) and improve your loading that way. If you get a few good clips, hold onto them. You can actually reload a magazine MUCH faster with the chargers than you can change magazines. It is not necessary to remove the charger from the charger guide: just slap the bolt forward and it flies off.
(Don't do that with those nice-feeding Mark II clips from World War One: they are just too slick to mistreat!)
Most important: have fun!