One ratio, one icon. The 1:390 listing belongs to the Boeing 747-200, the aircraft that made long-haul travel ordinary, reduced here to just under 18 centimetres of fuselage. That is small enough to display on a bookshelf or a window sill and simple enough to finish in a couple of evenings, since the parts count is low and the livery arrives as printed artwork rather than a masking exercise. For anyone who wants a Jumbo on the shelf without committing to a large airliner project, this is the painless version.
Odd ratios like this one exist because a manufacturer sized a kit to a box rather than to a standard. For a fleet with real variety, build from 1:144 aircraft kits; for larger, more detailed jetliners including Japanese operator schemes, see 1:200 aircraft kits. Even quicker civil builds are gathered under 1:220 and 1:288 aircraft kits.