Amen Florida, hard to make wood strips really work. You don't need a huge block of foam either. An inch on either side is fine--or even less. You don't even really want super-high density, just more than the EPS has. Everything flexes. The way to make a stronger area is NOT to make it rigid--that creates a stress riser. It's to make it progressively stronger as the structure moves toward the hard fin box. Restricted flex without delamination or crushing the foam under expected load is what you're aiming for. Wood strips distribute the load a little, but don't do much to keep the foam from crushing--too hard.