If the system says 75%, 90% or whatever it decides is best for runway length/weight/power etc, is this the figure always put in and used for take-off, or is it possible to add an additional figure as a bit of a safeguard (similar to approach/landing at Vref +5kts). As a paying piece of SLF, I'd be more comfortable knowing that the power used is slightly more than actually required to get us off the ground safely, rather than it just being sufficient?