Manually built Drag and drop exercise

I'm trying to build an exercise where people can drag and drop folded note objects onto an XY field, like post-its on a risk assessment chart.

I figured i won't be able to allow dropping at any position within one large target, as all the objects when dropped will snap to the center?

I thought I'd got around this by making a grid of 9 targets, which is just about enough resolution. 

I had it working yesterday! I built the trigger by getting it to increment a variable (which I don't really care about) when it dropped. At least I was getting started before a mass creation of triggers. I could happily drop. Now, it won't work and I don't know why.

If someone could help with:

1. Am I doing something that is actually possible?

2. Will it work if I populate 1 trigger for 1 item, with all the drop targets?

I have attached the story file.

Thanks!