Thanks to Vark111 for this tip!!!
The radar cross section of an aircraft is the "size" of the aircraft as far as radar is conserned. For example, the B-2 Spirit is a very large aircraft, but it has a very small radar cross section. As far as the radar is concerned, it looks no larger than a sparrow (the bird, not the missile). This feature is simulated in ATF, and can be accesed and edited with the help of ATF Toolkit. To edit this number, you need a text editor. The toolkit does not have a built-in RCS edit function, so it must be accesed by "other" means. Each aircraft has a *.PT file which is the definition of the aircrafts capabilities.
Open the PT file for the aircraft you wish to edit. The first section of the file is the "General" section. Lines 25 and 26 of this section are two numbers you are interested in.
[brent's_relocatable_format]
;---------------- START OF OBJ_TYPE ----------------
;---------------- general info -----------------
byte 5
word 605
word 568
ptr ot_names
dword $2bf3
word $4000
ptr shape
ptr shadowShape
word 0
dword 0
word 0
word 20
word -30
dword 0
dword 0
word 40
word 0
word 0
dword 0
dword 1972 <<---- This is the plane's avability date, by the way.
word 262
word 0
word 118
word 118
[[ word 100 ]] This is the IRS setting
[[ word 100 ]] This is the RCS setting
word 100
word 47
word 255
word 255
word 255
word 255
word 255
byte 27
byte 0
dword 26600
word 199
Line 25 is the aircraft's Infrared cross section. A large IRCS will create an aircraft that is easier to track and attack with IR missiles. Line 26 is the Radar cross section. A large RCS will create an aircraft that is easier to track and attack with radar missiles. Conversely, smaller numbers will make it more difficult to track and attack the aircraft with a particular missile type.