Hiya,
Well I'm still learning myself on this sort of thing but for mods each car normally has a positions file which tells the game where to place the driver, steering wheel, onboard camera views, etc.
If the data is wrong the driver looks like he's sitting in the airbox! Is this what you are referring to?
From there it becomes a little complex, each mod seems to be different in file layout. In some the positions file is living in each car folder.
So for example here is the positions file for a Red Bull Car (2012)
; ========================================================================
; GP4 Tweaker
; Car positions configuration by GP4 Central
; Red Bull RB9 by GeZeRe
; ========================================================================
[ARMS_POSITIONS]
driver01 = 0.0000, -0.0300, -0.1650
driver02 = 0.0000, -0.0300, -0.1650
[HELMET_POSITIONS]
driver01 = 0.0000, 0.1500, -0.1450
driver02 = 0.0000, 0.1500, -0.1450
[EXTERNAL_STEER_POSITIONS]
driver01 = 0.0000, 0.0000, 0.1200
driver02 = 0.0000, 0.0000, 0.1200
[REAR_LIGHT_AMBIENT01_POS]
driver01 = 0.0000, -0.1520, -2.6970
driver02 = 0.0000, -0.1520, -2.6970
[TYRE_POSITIONS_CAR01]
FrontRight = 0.7000, -0.2302, 1.2890
FrontLeft = -0.7000, -0.2302, 1.2890
RearRight = 0.7000, -0.2302, -2.1500
RearLeft = -0.7000, -0.2302, -2.1500
[TYRE_POSITIONS_CAR02]
FrontRight = 0.7000, -0.2302, 1.2890
FrontLeft = -0.7000, -0.2302, 1.2890
RearRight = 0.7000, -0.2302, -2.1500
RearLeft = -0.7000, -0.2302, -2.1500
[ONBOARD_CAMERA_CAR01]
Cockpit = 0.0000, 0.1333, -0.4571, 0.00, -0.70, 0.00
Driver = 0.0000, 0.1750, 1.2890, 180.00, 0.00, 0.00
FrontRight = 0.2900, 0.2860, -0.5950, 0.00, -3.00, 0.00
RearRight = 0.4600, 0.2000, -1.9500, 0.00, 0.00, 0.00
RearRightBack = 0.2700, 0.3900, -0.8000, 180.00, -15.00, 0.00
RearCenter = 0.0000, -0.1520, -2.6970, 180.00, 0.00, 0.00
RearLeftBack = -0.2700, 0.3900, -0.8000, 180.00, -15.00, 0.00
RearLeft = -0.4600, 0.2000, -1.9500, 0.00, 0.00, 0.00
FrontLeft = -0.3000, 0.1900, 0.2550, 127.00, -7.00, 0.00
Nose = 0.0000, 0.1700, 2.0590, 0.00, 0.00, 0.00
FrontWing = 0.3000, -0.3300, 2.0590, 180.00, 3.00, 0.00
TVCockpit = -0.0700, 0.5700, -0.5100, 0.00, -12.00, 0.00