Elf On A Shelf
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Hills are your best friend.
He's lovely, and if I had him I would definitely do the RIHS Amateur qualifiers with SHBGB. There are two classes normally, lightweights and smalls together, and middleweights and heavyweights together. Two of each weight/size qualify from each class, so you don't have to win to qualify. In my experience, going well for the judge is the most important thing. There are no mark schemes; the two judges confer and decide together, and it invariably seems to be a case of the ride judge stating his/her preferences and the conformation judge validating that or helping to make a decision with reference to conformation.
Definitely a wider noseband and straight top boots as AdorableAlice says. You can get nosebands up to 2 inches in width from Fylde saddlery online. I also would change the saddle for something a bit straighter cut at the front (whp style not totally straight as some judges have long legs and need somewhere to put their knees!), closer contact all over, and positioned further back behind the shoulder, but don't let that put you off entering with what you've got.
Colour in some pieces if paper of varying widths and stick them on your horses face one at a time, take a step back and decide which one looks best then go for that width.