I found a solution (at least it works 100% for me) I want to share it for those who still play this now an again:
- go to fallout.ini (in documents / my games)
- change the following lines:
iLocation Y=5
iLocation X=5
to:
iLocation Y=1
iLocation X=1
I tried it because the screen position seemed off after tabbing out and it's been fine since.