I was also looking for this when i started using Construct.
Like many other tools in construct, customization possibilities are very limited to specific use-cases.
Set image points and forget about the collision mask and its related actions altogether.
Gives you so much more possibilities.
Not just for picking points or ingame visibility, but for actual mathematical solutions for simply everything.
If you're going for something simple, that's great.
Otherwise stop trying to use the built-in tools because they're most likely not going to serve your needs.