I use a .775" core. When the sleeve is ready to install, I shave the tenon down to .750". IMO, the diameter of the tenon is irrelevant. The exception is weight distribution. The butt sleeve serves a bigger purpose than simply aesthetics. Case in point, a cocobolo nose with maple handle will be front heavy. The cocobolo butt sleeve counterweights the front for balance. The larger the tenon, the less the cocobolo sleeve will weigh, the less it will be able to counter the front tilted balance. Of course you can add weight bolts in attempt to manipulate balance. Contrarily, a maple front with cocobolo points & maple handle will not be near as front heavy as a cocobolo front. Using a larger diameter tenon in this cue makes sense to prevent the cocobolo sleeve from placing the balance too rearward.
These are often ignored details that I put a lot of thought into with a cue build. This kind of stuff is critical throughout the build from tip to bumper. Certainly somebody can dismiss it as wading in the weeds, but their success or lack thereof reflects their approach. Point being, put some thought into your cues. Try to grasp what's going on, why things get done the way they do. If you don't fully understand the purpose for each component and how it relates with the rest of the cue, then you are building blind. Further yet, if you don't understand the purpose, you cannot figure out ways to make it better. We have plenty makers who build a so-so hitting cue that are really pretty. Don't be another one.