6foottanker,
You have kind of answered my point. Had the tanker turned left, even a little bit in the time allowed, the F15s would have crossed the nose further away. Its all to do with collision geometry and how to visually recognise and then break a collision.
I am an advocate of TCAS, however, sometimes there is too much reliance on it. Obviously, tanker pilots are used to operating with many "fast movers" operating near to them. There may be an assumption that ALL are visual with the Texaco but this is not always true. Being "heads out" on both sides of the cockpit is still of vital importance.