Balance Field Length
Airliners and every operator/pilot working under part 135 or 121 will have to comply with performance compliant aircraft. That means that you are working on a balance field length philosophy, ie at a certain speed (V1) you would have made a decision to either continue the take off or reject. Thus regardless of runway behind you or not, if your aircraft reaches V1 the decision was made already. Now if the length of the runway falls withing the balance field length criteria (to accelerate to V1, reject and stop within the remainder of the field + the stopway, with the most critical engine having failed at V1) it does not matter if there is half the runway behind you or not.
Hope this clarify the issue