I believe it starts counting with the tile the constructor is in. This is actually why we added the lines, it was do nebulous to see the range without them, and we don't want players having to count them.
I think it is a bug, as your way would make the full hexes to the right and left out of range even though they are completely in the circle.
I know the next hex right and the next one left are not in range as they are in the sixth hex even though the circle cuts through them.
I believe this is what is happening to the hex in question even though it is in the fifth hex and "should" be in range, thus a bug.
@Illauna All that said your placement of the Starbase was not optimal the only possible reason to place it that far from the resource would be ship range and one hex is not worth missing it. You will have a tech later and there is an ideology perk that will increase SB range and you will get the resource latter. You will miss out on "improvements" though.
