I'm trying to 'inset' a path a fixed amount, so that if I were to then increase the stroke width, I would end up with exactly the same shape. I understand that in some cases this just isn't possible, but I'm having trouble making it work even in really simple cases.
When I use the inset tool on a simple triangle (right) this works perfectly and does what I'd expect until the shape itself gets smaller (the image is created by repeated duplicate & inset).
However when I use it on slightly more complicated shapes like the two on the left, curves are very quickly introduced into shapes that never had them, in seemingly random places:
In each case I've drawn the shape with the straight line tool, but this happens even if you draw a rectangle (and in a non-symmetrical way):
Perhaps I'm using the wrong tool for the job - but if so, is there another tool or extension that'd do what I want?
Note: This looks like a similar question to Outset small rectangle path in Inkscape without round distortion? but dealing with insets. Changing the inset/outset amount as suggested there hasn't really improved matters for me.
... I could use blend to get an image like in the examples, but this is just to demonstrate the issue. In reality I just want to take an object, convert it to a path, and then shrink that path so that when the path is (for instance) 1mm wide, the object has about the same outline as before.