The best way to know for sure is to just go to training mode and see for yourself, I'll do a quick summary here, but yeah.
I believe the bugs will be in a set spot when you release the button, so if you're moving forward with say j.6c or j.236c and you're trying to hit them with a bug that comes in from the middle of the screen, you may want to try releasing it while holding 6.
Anyway, to the summary.
I'm using the starting positions of a match as reference to the characters. Arakune is player 1, and I have a Jin set up as player 2.
5a: All of the a bugs come in at an arc from the 6 side of the screen. the top of the arc is roughly the
middle of player 2's health. Comes down and lasts just behind Arakune.
4a: The top of the arc is just off screen above the time limit. Flies way past Arakune and lands off screen on the 4 side.
6a: The top of the arc is above the first few percent of player 2's life. Lands right in from of player 2's feet, it didn't hit Jin, (the person I have set to player 2) but it looks as if they were any taller it would hit them. I prefer this bug when using a.
5b: Comes in at a ~45 degree angle from the top of the screen from 4 to 6. Passes through halfway of player 1's life, and lands on the ground at about half way of player 2's life.
4b: Comes in at a ~45 degree angle from the 7 corner of the screen. Lands just short of the middle of the screen under the time limit.
6b: Same angle comes through about at the 30% mark of player 2's life, lands off screen on the 6 side.
5c: Comes up from the ground, behind player 2's starting position, hits him, and lands just short of the middle of the screen. The bug travels from 6 to 4
4c: Comes up a little 6 of the middle of the screen, and lands a right before player 1's feet/blobby appendage.
6c: Comes up from right below player 2's character portrait on the life bar, hits Jin's feet, not sure who else it hits/doesn't hits.
5d: Comes down from the top of the screen and a parabola (upside down arc) around the last few percent of player 2's life. It hits Jin if he's standing at the starting position. The d bug leaves the screen around half way through player 2's life.
4d: Comes down at the 20% mark of player 1's life, moves right in front of Arakune, and leaves between his life and the time limit.
6d: Comes down roughly around the 80-90% mark of player 2's life bar. Comes down a good bit 6 of player 2, and exits above player 2's character portrait.
Hope this helps.