Weird thing about FreeSync over HDMI

I have a FreeSync monitor (AOC G2260VWQ6), and a R9 280X, in theory it's all perfect for me to use FreeSync but the problem is this:

I have done perfectly every step of the guides out there to get the FS over HDMI and I still dont get it. Tried everything on CRU and nothing, I don't know what more to do, is there any secret or this monitor just doesn't support it over HDMI?

And yes, I could use DP but the thing is that my 280X uses mini-DP and I have a normal DP.

Thanks, I'm new here.