ABC News (Aust) states - "China said the objects were spread across an area with a radius of 20 kilometres, in sizes that appeared to be 13 x 18 metres, 14 x 19m, and 24 x 22m."
If the fuselage and wings opened out on impact, this would explain the large sizes of the items sighted. Those sizes eliminate sea containers.
Items were stated to be "floating", possibly just below the surface? Light refraction under the water could account for variances in size estimation.