I believe the "dead zone" turns out to be pretty insignificant, because the difference between close angles is pretty negligible do to of the nature of a circular input which is converted into a component of the perpedicular distance from the launch angle. What I'm trying to get at it's the sine/cosine of the angle that determines the angle like if the launch angle was 0 then to get an angle of 18 it'd be:



18 * sin ( 90 deg ) = 18

and thus for other angles...

18 * sin ( 89 deg ) = 17.997

18 * sin ( 82 deg ) = 17.8

18 * sin ( 70 deg ) = 16.9

18 * sin ( 45 deg ) = 12.7

18 * sin ( 20 deg ) = 6.2

18 * sin ( 0 deg ) = 0



What I want you to notice is that the values don't change much for the partial DI just because you are off a few degrees. Being off by one degree will change your launch angle by 0.003. Being off by 8 degrees only makes a difference of 0.2 in your launch angle. You have to be off by about 20 degrees to see real significant effects in your DI at which point your angle will be effected 1 degree.



Since You can hit 0 and 17.3, in the case you needed to DI 8.45 to be perfect, choosing either of those options will only effect your DI by 0.2 degrees, so you shouldn't concern yourself with it. It's why we've never noticed you can't DI some moves the full 18 degrees difference. You can DI 17.8 at least so you're not going to miss the small drop-off.



I hope this makes sense as I feel I'm having a little trouble explaining it thoroughly.



Also another thing to keep in mind is that you cannot DI fully in most directions because the octagonal shape prevents you from holding the stick fully extended. The consequence of this is that DIing in the notches instead of the exact "ideal" angle around the notches may just as good or so because it's really the distance from the axis of the launch angle that matters rather than the launch angle (on a circle this would be the fully extended perpendicular angle, but on an octagon it is not so straight-forward).



And one more thing concerning survival DI: The best DI is not always the "ideal" DI shown here. The issue is that you really want your trajectory to send you to the corner as much as possible. The "ideal" DI is a great guide and about as good as is realistic, but for an example I was testing when dthrow -> knee is a guaranteed kill on Puff and I found that using the exact angle that is perpendicular to the knee's launch angle was not always best because that DI actually sent Puff off the top blastzone while DI'ing "less" could help Puff survive by shooting Puff right into the corner. There are a lot of factors to the optimal survival DI, but the difference between the convential wisdom survival DI and "perfect" survival DI is about 5-10% depending on the stage and move and such. It's not likely to be the difference in winning games very often.