Shim the drive side to get the best line you can achieve in
#4 or
#5 cog (since you don't have a 'middle' with an 8-speed cluster) - - with as little shim as you can get a way with. Then add one to the non-drive side if you still need to take up some slack. Chainline to the big cog is just going to be what it's going to be - - set for middle.
BTW, check your BB bearings after a season and make sure they're clean and still spinning good. The stock RF X-type BB has that same awful plastic dust-cap/spindle interface that FSA externals have (so that they can cheap out and use standard 20mm ID bearings with the 19mm spindle. The dust-cap eventually at least partially fails, letting crap and corruption into the bearings. If they get notchy, replace them with a proper 19mm ID Enduro bearing set.