I think the mock up is close to the length and width of the E-2 using the J-15 as reference. The real E-2 is only 17m long, about as long as f/a-18c, much shorter than the F-14 or Su-27. This is similar to how the mockup compares to the J-15.
Remember the su-27 family has spawned 2 side by side twin seaters, the Su-34 and Su-33UB. The fuselage of neither are appreciably wider at the cockpit area compared to the single seater. The cockpit area of the mockup is similar in width to the j-15.
Almost the entire fuselage of a E-2 style AWAC is pressurized crew space. The crew behind the cockpit sit in a single row facing one side. Even if we give each crew member a generous 2 meters of space, In a 17 meter long fuselage, there is plenty of room behind the cockpit for 4 more crew sitting side by side facing to one side of the aircraft down the length of the fuselage.
Remember the su-27 family has spawned 2 side by side twin seaters, the Su-34 and Su-33UB. The fuselage of neither are appreciably wider at the cockpit area compared to the single seater. The cockpit area of the mockup is similar in width to the j-15.
Almost the entire fuselage of a E-2 style AWAC is pressurized crew space. The crew behind the cockpit sit in a single row facing one side. Even if we give each crew member a generous 2 meters of space, In a 17 meter long fuselage, there is plenty of room behind the cockpit for 4 more crew sitting side by side facing to one side of the aircraft down the length of the fuselage.