BF support bearing query

[Voicecoil]

All the pics (Hiwin and clones) I've seen of the BF support bearing show the end of the ballscrew almost flush with the end of the bearing see my little sketch:

However there's no dimension given for it's exact position in the mount, even in the Hiwin book. I guess there's a certain amount of freedom of movement in the BF as it's billed as a support rather than fixed bearing, but I'd like to get the initial position more or less in the centre of the allowable range, and do I need to leave some space outside the bearing in case the end protrudes a tad I wonder? Any wisdom/experience on this would be gratefully recieved, thanks.