9-8 is considered more than 1/2 a ball, almost a ball.
Lou Figueroa
I think Jay's assessment is more accurate than yours.
The higher the ball count the spotted player needs to run to, the less of a spot it is.
So, if 8-7 is roughly a ball spot, 9-8 would be fairly significantly less. I would judge 1/2 to be about correct. I've gambled a little giving spots in One pocket, and I would be significantly more confident giving someone 9-8, as opposed to 8-7.
About a half ball more confident.
Short Bus Russ