It's not supposed to go above 18. 18 is the highest amount you can influence your trajectory by. t - t0 is trajectory - your DI
For example, let's say you're DIing a move that sends straight up (90) to the right (0).
I'll use a more accurate formula that uses absolute value bars in the sin² argument and takes into account that a 45 degree angle input is 0.707, not 1.
the cos(t0) changes to sin(t0) in cases where the input angle is between 45 and 90. (or any comparable angle on the unit circle)
18cos(t0)sin²(|t-t0|)
18cos(t0)sin²(|original trajectory - trajectory DI|)
18cos(0)sin²(|90-0|)
18*1*1
18 is the resulting difference from the original trajectory. Your new trajectory is 90-18 = 72
Or Falco's dair, where you DI at 20 degrees.
18cos(t0)sin²(|290-380|)
18cos(380)sin²(|-90|)
18cos(20)sin²(90)
18*0.93969262078590838405410927732473*1
~16.91
~17
290 + 17 = 307
Some other things come into play with DI though, like the fact that the place where the control stick is isn't perfectly circular. Sometimes, going into one of the notches even though it's not perpendicular is better because you have more absolute distance from original trajectory that way.
Toph: falcon's knee is indeed 32, and Sheik's fair is 25. Falco's dsmash is 25, his Dair is 290, Doc's bair is 28, Falco's shine is 84, Fox's shine is 0.
Link's ending hitboxes on his Up-B are 0, Pika's tail spike is 0. Anything else anyone want to know?
It's important to realize that forward is considered 0.