Sophos UTM Cloudflare SSL Issue

Hi

I've recently discovered Sophos and started evaluating UTM, it seems great & I would like to adopt it into my setup

Currently my web server doesn't have a certificate for SSL and has used CloudFlares built in SSL encryption as part of its service

What I found in switching over to Sophos UTM was I would get a Bad Request (Invalid Hostname) error intermittently, generally while browsing the site in https (most browsers seem to want to revert to SSL even if you explicitly specify http)
My initial suspicion is this appears to be a conflict between the passive SSL service of cloudflare and UTM then trying to do it, although it is very possible there is more to it

Because of the popularity of both I'm hoping this will have been experienced by someone in the community that might be able to offer an insight to what the problem is, or any pointers on how to best implement the two

I've looked through the manual in respect to taking a number of approaches & not come up with a great deal that helps, I would be grateful to anyone who could point me in the right direction

Many thanks!