IMPORTANT: The following applies to V1.12. The files in V1.02 are different. And, yes, you must set it for each aircraft's cockpit. There is no global setting that I'm aware of.
The place to set the default zoom for TIR in the cockpit differs depending on whether or not you have the Z-axis (the "zoom" axis) enabled. With it enabled, the setting lives in view.lua. Change the 2nd number in the "Camera views angle limits" section for each aircraft.
-- Camera view angle limits {view angle min, view angle max}.
CameraViewAngleLimits = {}
CameraViewAngleLimits[PlaneIndex.iSu_27] = {20.0, 170.0}
CameraViewAngleLimits[PlaneIndex.iSu_33] = {20.0, 120.0}
CameraViewAngleLimits[PlaneIndex.iSu_25] = {20.0, 120.0}
CameraViewAngleLimits[PlaneIndex.iSu_39] = {20.0, 150.0}
CameraViewAngleLimits[PlaneIndex.iMiG_29] = {20.0, 120.0}
CameraViewAngleLimits[PlaneIndex.iMiG_29K] = {20.0, 120.0}
CameraViewAngleLimits[PlaneIndex.iA_10] = {20.0, 170.0}
CameraViewAngleLimits[PlaneIndex.iF_15] = {20.0, 170.0}
Without the z-axis enabled--in other words, you use the keyboard or a joystick slider or whatever to zoom--the default cockpit zoom is set in snapviews.lua. It's the 'viewAngle" setting for the #13 position for each aircraft. (Example: Snap[1][13]["viewAngle"] = 117). BTW, this number also controls the default cockpit zoom when you are not using TIR as well.
In case you're wondering, the flyable aircraft are identified by number:
PlaneIndex = {
iSu_27 = 1,
iSu_33 = 2,
iSu_25 = 3,
iSu_39 = 4, -- Su-39 or Su-25T
iMiG_29 = 5,
iMiG_29K = 6,
iA_10 = 7,
iF_15 = 8,
Hope the above is sufficiently clear. Experiment and find numbers that are comfortable.
Rich