Court case
I hope that the judge will first attend a course on aircraft performance!
A performance calculation gives you the maximum mass that you can lift off the runway at prevailing conditions.
If your actual mass is less than that maximum, you can use your margin to take-off with less thrust, to lessen engine wear. You can eat up all your margin, or nothing at all. How much margin you eat is company policy, not a matter of the law. (Meaning, you are free to choose any assumed temperature between full thrust and the maximum temp that you have obtained from the performance table).
The above statement is valid for dry and wet runways!
If the runway is wet, your lift capability is disappointingly low. The lawmakers have decided that is is allowed to improve lifting performance by allowing a lesser obstacle margin (for the engine failure case). Notice that, in wet conditions, it is allowed to take off at reduced thrust.( Some could argue that that is in contradiction with the lowered obstacle clearance).
The performance problem with a wet runway is not in the acceleration part of the takeoff, it is in the deceleration in case of a stop. The V1 has to be low to enable a stop on the remaining runway. From that early V1, acceleration to takeoff speed takes longer than from the (higher) dry V1 speed, so the stop distance and the go distance will be approximately equal again (balanced).
(A takeoff does not need to be balanced because it looks nice, but because, if it not balanced, one scenario (STOP or GO) gives excess performance, while the other scenario is very limitng. Balancing both scenarios gives approximately equal masses for both scenarios, so it gives the best overall performance - remember, you are alwas limited by the most limiting factor. Besides stop and go, also climb performance is evaluated, and could be the more limiting factor on hot and high airports with a long runway).
Using wet figures usually necessitates a lower maximum of assumed temp for a given takeoff mass (that is the flip side of a lower maximum T/O mass at maximum thrust).
A lower max assumed temp means that the thrust to be used is higher. Now, if you use WET figures on a DRY runway, at the max assumed temp that is allowed by the wet table, than you will use more thrust than you would need on the dry runway - you have more margin than required.
THE ONLY THING THAT YOU MUST NOT DO, IS TO USE THE LOWERED V1 OF THE WET PERFORMANCE, BECAUSE IN CASE OF THE DRY RUNWAY YOU MUST MEET THE HIGHER OBSTACLE MARGIN REQUIREMENTS.
End of lesson.
Any questions?