Need some advice on bridle size

So I splurged on a PS of Sweden bridle for Nilla. Her best way of going is in a hackamore and a spidepull. It's basically a double bridle without any bits.

Double Bitless Bridle
She is absolutely terrible about bits. She gapes her mouth, throws her tongue around and really likes to stick her tongue over the bit. When I tried her out before buying her, the previous owners used bailing twine to tie the bit over her nose so she couldn't put her tongue over it. It's an effective trick, but it's not a solution to the problem.

You thought I was making it up, right?
Even with a flash tightening as much as possible, she finds a way to stick her tongue out. She's also very distracted and spends more time fighting the bit then paying any attention to the rider. I have tried tons of bits. One trainer actually pulled out a giant rubbermaid bin filled with bits and we tried lots of them. She doesn't like anything that's a bit.

With just a hackamore, she's very hard to steer. With just a sidepull, she'll basically pull your arms out and run off with you. When I first put them both on, everyone thought I was crazy. Then I started riding around and getting her to bend and listen. The next day the trainer rode her and was exclaiming over the genius of it. Prior to this she hadn't felt comfortable cantering Nilla, but this bridle combo made her feel like she actually had enough control to not die.

However, outside of myself and the trainer, no one who rides her knows how to use a double bridle. Even my husband just sort of mashes both the reins together and hopes for the best.

Due to The $900 Facebook Pony's postings, I was wanting a PS of Sweden bridle. I was planning on getting the cool noseband bridles to address Nilla's gaping issues. And then I saw that they make this:
Cavemore Revolution
It was like they knew us and invented it just for Nilla. So I put the bitted bridle plan on hold and ordered this piece of brilliance. 

I was very torn between the cob and horse size. I have a cob bridle that fits Nilla on one of the longest holes. I also have a horse bridle that fits on the next to last highest hole. I also had to drill about 10(!) holes into the horse sized flash band on her one bridle to get it to fit. So she's pretty clearly in between the two sizes. The real deciding factor for me in picking cob sized was that I got a hackamore a few months ago for Nilla and the noseband was way too big. I actually had to swap hers and Dijon's hackamore nosebands to get it to fit her. So I figured I better get a cob sized in this bridle.

 I've been following the tracking obsessively and it finally arrived today so I unbagged it and went over to the barn to try it on right away.

When I tried it on her, I was starting to panic as it seemed too small. Everything is on the largest hole and it just barely fit on her. I thought the under jaw strap was way too far back and the hackamore itself too high up. However, when I got home and could look at the PS website (no cell reception at our barn), it looks like it's perfectly sized.

I took a ton of pictures of a very fidgety mule - this was the best I got
PS of Sweden Model Shot - for comparison
I am also going to email PS of Sweden because I absolutely adore this bridle. I love the quality of leather and all the other details I want to do in another full post, but I'm not sure if I should get a larger size. However, I thought I'd consult the internet hive mind.

Please let me know your thoughts on the sizing in the comments. I really appreciate it!