
That is the furthest into the curve I can place it. There is also one slot to the east/right (from screenshot perspective) that is also "too close" to the curve.
I'm not sure if Squeak Through affects rail collision boxes, but I did have it enabled at the time when I observed this behavior. (Also Beautiful Bridge Railway and Naked Rails, but hovering over the rail pieces in the screenshot shows no yellow mod name text, so I don't think any mods are changing the vanilla rails used here.)