X account can boost/or raf...but if X is a lvl 80 the chain will not work between X-A because there is too great a gap between lvls for the toons. But the chain from A-B will work so you have nothing to worry about.

Now if you decided to start a brand new 5-man team at lvl 1, then the chain from account X-A will work. Bottom line, that is the correct setup to chain accounts.