Use a wider capture band for placing notes into chords
Currently SP turns the cross hairs red when the current note is being dragged on to the previous note to form a chord. When you move the current note close enough to the chord position, the current note "snaps to" the chord position, and the cross hairs turn red. The red color is a nice touch.
But the current width of the snap-to capture region is not optimal because it takes too much delicate maneuvering to place the current note exactly on the chord position. It's too easy to undershoot or overshoot, and it's too easy for the current note to slightly shift position when you lift your finger, so it falls out of the capture region and you have to start over again. Creating chords within a triplet or quintuplet structure seems particularly tricky.
A better approach would be to make the red-line capture region wider (should be a trivial parameter change in the code).
If this change was made, it would be easier to place notes into chords, and harder for the placed notes to fall out of the capture region when the placing finger is lifted off the screen.