I don't know about SCI and CoG but I am running 2.25". The thing is as Chad and SCI said, setting it, depends on a lot of things. If you change you back angle even slightly, that can affect your balance. Small changes can have large affects. I hope your chair is adjustable if you are still deciding on your CoG. I suggest making small changes. By the way, a lighter front end (tippier chair) will making pushing easier but you give up stability. I want to be one of the cool kids and go with 3.5 or more but I hate falling backwards and have done it a few times. I go for stability.

Choosing CoG is a complicated thing because it also affects your pushing and comfort. Get lots of info and try different settings. I've had friends with settings that seemed crazy but, it worked for them. One friend had a front end so heavy, while in it I couldn't pop enough wheelie to move the castors off the ground at all. It was like he had a sack of cement up front but, he'd lived that way for years, traveling all over the country and the world. He knew what he was doing. Another friend had a super light front that came up whenever he pushed. Settings are personal, find what works for you.