It's not quite as easy as it sounds, though for the speeds at which we operate models it is fairly straightforward. The net thrust, exhaust velocity minus intake velocity falls in pretty much a straight line from static value at no airspeed to zero thrust where airspeed equals exhaust speed. So for example if static thrust is 20lbs and exhaust speed is 800mph, net thrust at 400mph would be expected to be 10lbs. But, there is another effect, that of the intake ram air effect which does much of the compressor's work thus freeing up much of the energy to be used as thrust instead of driving the compressor, thus increasing the thrust. This starts at zero with zero airspeed and rises exponentially as the airspeed rises. The net thrust is the combination of these two effects. Initially the thrust falls as forward speed reduces it and the ram air effect has little power. As speed rises the thrust contrinues to fall but the ram air effect becomes more powerful and eventually its increase matches the decrease caused by exhaust:airspeed difference and the thrust has reached its minimum point. Above that speed, the ram air effect rising exponentially is going up faster than the straight line decrease from exhaust speed is going down, and thrust rises again back up to and even over the static level.

At slow speeds therefore the reduction in thrust will be almost straight line towards the zero point because the ram air effect is negligible. For most of the speeds at which our models operate then, the reduction in thrust will be fairly straight line, barely moderated by the ram effect.
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