https://grey.colorado.edu/coin3d/classS ... ea24bb6dba
So, changing the pick radius should also affect the image selection.
I am able to select them but doing this is in the 3D view is very tricky. You have to hover over the icon to see it highlighted in a certain mouse position and then it's selectable.Perhaps this solves an issue, of which I'm not sure if it exists on MacOS only - or while working on it you may have look?: When two constraints are placed at he "same" position, none of them is selectable with the mouse.
I attach such a file, I cannot select point-on-object nor the orthogonal constraint.
The easier way is to simply select them on the left side in the Constraints panel.
With your T-sketch I wasn't able to select the perpendicular constraint icon on top of the point-on-curve constraint (on a weird mouse position). But I was able to select the latter and also the perpendicular icon on top of the vertical constraint icon could be selected which automatically selects its sibling.Also, when constraint icons are merged into a single icon, Coin is only responsible for selecting the merged icon, it can't select individual constraints
And as said above all three icons can be easily selected inside the Constraints panel.