We have two blue dots, which one should I use?
If you want to make the cable length to be minimum, you should definitely choose the closer one to the red point.
You mean closer when we go clockwise starting from the red point.
Correct.
What happens if I do not care for the cable length?
In that case, you can choose whichever you like. If you choose the blue dot on the upper half plane, the impedance Z there will be 50+jX [ohm], where X is some positive number.
Or if you choose the blue dot on the lower half plane, the impedance Z will be 50-jX [ohm], where X is the same as before.
Which means?
Which means, you put some capacitance in series in the former case, and some inductance in the latter case.