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Take a simple practical example. Take a cardboard block or anything cuboidal in shape like that you have. Try to bend the block at two opposite rectangular faces of the cuboid. It is easy. But, try so taking the other two rectangular faces. If we assume that the distance between the first two faces is LESS than the last two rectangular faces then it is gonna be even more difficult. If we replace it with a cylinder, the thickness or the interface distance would become the diameter. As Young\’s Modulus is directly proportional to easiness in bending or changing configuration and bringing it back to original, and this bending property is inversely proportional to thickness, Young\’s Modulus is inversely proportional to root of diameter or simply, diameter.