[HELP] Lasting boot issue

Hi all,

Firstly, I've read through all of @Wiredsport's post regarding measurement and I measure up to:
263 Mondo (8.5 US Men) and I've gone ahead and measure my width too.

Left Foot: 10CM
Right Foot: 10.3CM

I currently ride a 8.5 Burton Photon and the length of it is great, no toe issue and heel hold is pretty decent however after 0.5 - an hour of riding, there's pain in the area highlighted below. After a 3 hour session, I can barely walk in the boot getting back to my car/hotel as that specific part is just pain, and its more of a bruised pain.

I already have the boot heat molded and also have custom insoles for my extremely flat feet, most of my running shoe exhibit wear and tear that shows that I usually over pronate due to my flat feet, hence the area that is highlighted above usually "pushes out" against my boot/shoe.

I've been to the local stores and when they measure they claim that I don't really have a wide feet and don't need a wide boot yet going of the chart itself seems like I'm bordering on E? I'm pretty much out of ideas and was wondering if getting a wider boot might solve the issue or make it less painful.