These are Pakistani airbases.
Except Pasni airforcebase in Balochistan, each airbase is with in 400 km from Indian border.
90% of Pakistani airbases are within 300 Kms from India border.
If S400s are place 100 kms in Inside India border, along an axis parallel to Pakistan, as you claimed in your post.
Each and and every aircraft, taking off or landing on these bases, will be at a potential risk of being shot down.
For Babur to target S400 , Pakistan will need exact location of S 400 components because.
1. Because Babur is not a anti radiation missile.
2. Damage radius of a cruise missile like Babur is only couple of hundred meters.
It will hard to get exact location of S400 components.
1. Because Pakistani recon flights over S400 batteries, will be shot down.
2. S 400 is a mobile system, its component can quickly change their location.
3. Pakistan does not own any real time, imaging satellites.
Even if, Pakistan some how manages to get the exact co-ordinates of S400 components. 9M96 missiles of S 400 family has been specifically designed to engage low fly cruise missile.
Even if 9M96 missile fails to engage Babur , there is always Pantsir S1 point defense cannons, protecting S 400 components from low flying threats.
Where as my sources are not imaginary and can be presented to other posters.