It is not really relevant what the differences are between the two. The simple fact is the "Gold Ring" must be 100% X & Y centered over the centerline of the tripod.
The focus ring should be clamped so it doesn't turn (But only after you "tape" it on "true" infinity and switch the lens to "manual" focus). Auto focus is not possible with the RingT and really because the Sigma 8mm is such a great lens it pretty much is always in focus anyway.
As I don't have a Nikon mount Sigma 8mm I cannot give you exact positioning. The images above were supplied to me long ago by Agnos.
Get the "Gold Ring" over the tripod centerline and your in business. (Simple as that!)
P.S: Your lower image is that of a Canon mount Sigma 8mm.