I need some help with mounts for a clip on thermal to be used with a red dot

I just purchased an OFN640+ thermal that will be here within the next week. From everything I’ve read it’s made with similar/the same components as an RH25 v2. I have FaceTimed the buyer and from everything I can tell it seems like a good unit. I paid $1800. Anyway I’m trying to set this up as a clip on thermal for my AR. I’m currently using an Aimpoint T2 red dot and magnifier on a unity FAST mount. Optic center line is 2.25”. If I use a Wilcox flip to side mount, what riser height should I need? I’m having trouble figuring this one out. Here is a link to thermal: https://www.fotonika.online/product-page/ranger-640-ofn640-thermal-sight

Does anyone else have similar setups that can share? Thanks