question about avoiding obstacle

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this image is very informative and helps understand what is going on in your costmaps:

1 - It is unlikely that your collisions are caused by the robot radius parameter, as I understand you set bot the circumscribed radius to be larger than reality and the same goes for the inflation radius.

2 - Firstly, in normal situations the robot should never plan or enter the zones below the circumscribed radius. Then you can set the inflation radius which, as shown in the figure below, is a buffer zone. One way to understand this buffer zone is: the robot can enter this zone if necessary, but it would rather avoid it. As not getting too close to walls unless in a narrow passage, for example. The cost_scaling_factor will determine how the costs are distributed in the buffer zone. As an example, they can fall abruptly or slowly after the circumscribed radius, reflecting your preference on how close from an object you are willing to go if necessary.

3 - I propose you create another question about this. This is related to your local_planner, and the interaction among its parameters, which is another subject.

extra references: costmap inflation robot-clearance-from-walls