As you will know, the chart shows that 29" column includes 29.5" as does the 30" column.If you use the 30" column you will get a stiffer shaft.
Perhaps the thing to do, is look at your arrows and see which of the columns they came from. I found
ACC 3-28 in T7 and T8.
T7 and T8 appear at 29" and 30" for 41-45lbs draw weight.If your holding weight is less than that, I guess you chose T7 from 30" column.( T8 would be 31")
If your holding weight is more, I would guess you reached T8 from 29" column.( T7 would be from 28")
If your holding weight is 41-45lb you could use 29" and 30" columns and find
ACC appears as 3-18 and 3-28 in T7 and 3-28 and 3-39 in T8.
It shows that 2-28 is suitable which ever of the two columns you might have used.
Perhaps then, the answer is to look down both columns and find the appropriate T numbers. Then find which shafts appear in both, and go for those.