With the Grid Graph Settings as in this picture, I thought it meant that each node represents a size of 0.1 x 0.1 units of space. The Collision Test is set to Capsule with a Diameter of 0.45. However clearly there is a path calculated which passes the 20cm (0.2 units) gap.
Update: Could it be that the reason for this is that the node size is affecting the collision test? When I set the collision diameter to 4.5 instead of 0.45 for a node size of 0.1 it seems to behave as expected. I thought the node size should only affect the amount of nodes and therefore the grain of the grid?