This level is completed basically using lots of fan and rebound shots. For most levels using this block layout, I usually fire a fan-and-rebound to the bottom wall first, in attempt to hit the tanks in the lower right quadrant. This may or may not succeed, but it has an equally important effect – it prevents those tanks from entering your quadrant. Speaking of which, that is usually what the tanks in the upper left quadrant will have done by this time.
When the tanks from the upper left quadrant has entered or are entering your quadrant, some of your previously fired shells should have expended themselves, leaving you new rounds for defense. Use the usual tactics of leading and fan-and-rebound from then on.
Be patient and avoid the two upper quadrants altogether, as in the heat of battle, the yellow tanks can lay mines behind the two triagular barricades unbeknownst to you. Obviously that’s dangerous. When you are left with tanks in these quadrants who aren’t willing to come down, use fan-and-rebound shots to get at them.
Next: Mission 10.