Alas not - that is just the way it is unfortunately. Basically it is the collision of two different worlds - theoretical performance and real-world failures. The assumptions for theoretical performance are that the QRH assumes no thrust reversers and a non-factored landing distance. The LPC, however, assumes both thrust reversers are functioning at full reverse power every time and applies a 15% margin to the landing distance. The problem at the moment is that when you have, for example, an engine failure, it has no ability to then automatically recognise that there will be thrust reverse available on one engine only. The situation is further complicated by the fact that there is no calculation available for idle reverse thrust - it is all or nothing. That is not so bad if you use autobrake as they apply a deceleration rate which is modulated for thrust reverse - ie if you apply more thrust reverse the autobrakes will apply less braking power to maintain a certain predetermined deceleration. It is still not really very satisfactory and does not generate that warm fuzzy feeling we all want to feel knowing that the calculation is an accurate reflection of reality. It is, however, the best it can be and much better than the QRH. No doubt in time these problems will all be sorted but in the meantime it is important to understand the assumptions being made before relying on the calculations without thought.