Uh, spotting is a visual term. Visual size for a "stealth" aircraft are not the key factor.
Spotting factor is a technical term that concerns how much space on a carrier deck is consumed.
2.4 would mean that you give up 24 F-18s for 10 F-22s.
Someone needs to do some homework.
http://ocw.mit.edu/NR/rdonlyres/Aeronautics-and-Astronautics/16-885JFall-2004/1ABA501E-4F31-4EEE-AEEB-123274492635/0/flight_controls_1.pdf
Look down to page 9.
To help your education.