Fine-tune collision scale?

I’m having to add collisions to a tree mesh myself and I’m having a little bit of trouble getting the scale right. I’m using a capsule to make it as simple as possible and when using the scale tool I can’t get it small enough to fit the stem of the tree, the scale is either twice as large as it should be or way too small.

Is there any way to fine-tune this? I can’t find any scale parameters for the collision box anywhere.

And of course after spending almost half an hour kicking myself over this I find the answer 10 seconds after I ask the question, top right corner → scale grid snap value. Doh!

even that could not be enough sometimes…