As far as I can tell, icons snap "up" (and only up) to the nearest grid, even if they are placed only 1 pixel above the center of the row they are placed in. This often means that I have to switch to another desktop and back to make sure an icon stays where I put it.
If I understand how Dexpot does this (please correct me if I'm wrong!), a simple fix would be to offset the horizontal lines of the detection grid by half the height of the icon. In this case, dropping the icon anywhere within the desired final square in the grid would place it at the center of that specific square.
I don't think I've ever had a problem with horizontal jumps from one column to another, only vertical jumps from one row to another.
Do I understand this properly, and does what I say make sense?
And thanks for an awesome program! I searched for quite a while before finding one that did everything I needed it to... and what I found in the end is really sweet...