Size 6 e3 loses (Y)
e3 and symmetrical moves (c5, e5) are losing moves even if the swap rule is disabled. Blue answers d5.
Blue threatens to win via b6 reduction (or e6). The threat's carrier is shown.
Blue also threatens to win via c5 reduction (or e5).
So Red must play in one of the hexes that belong to the carriers of all four threats.
Solution to intrusion at b5, b6 or c5
If Red plays at b5, b6, or c5 (or all three), Blue plays d4.
On the left, 2 is connected to the edge. On the right, Blue now has the following 3 threats:
Since the threats don't overlap, Blue wins. In other words, Blue had a corner template.
Solution to intrusion at c6
If Red intrudes at c6, Blue plays c5.
The rest of the solution is very similar.