Four, as shown in the figure, $R$ is a square grid composed of 25 small squares with a side length of 1. Place a small square $T$ with a side length of 1 on the center square of $R$, and then place more small squares with a side length of 1 in $R$ according to the following requirements:
(1) The sides of these small squares are parallel or perpendicular to the sides of $R$;
(2) Including $T$, no two small squares have any common points;
(3) For any two small squares including $T$, there must be a straight line passing through them (including edges) that is parallel to one of the sides of $R$.

How many more small squares can be placed in $R$ besides $T$ while satisfying the requirements? Prove your conclusion.