I think that isn't very realistic. First, if your soldier is crouching, it is supossed to be in guard, so, any thing that moves will come under a rain of bullets. That is the same for snipering.
So, i think that reaction time could be a measurement of TU, Mind and speed. For example, take the enemy TU spending and compare with the Speed units of the soldier x2 and divided for 10.
Soldier speed stats: 23 the reaction coefficient is 4.6 or 5 points.
Enemy walks three steps; 6 points TU
6 points are more than 5 points, so, the soldier react at this (speed). But, if the enemy walks only 2 steps (4 points), he can shot first. But now, the enemy uses 16 TU shooting, this will be 1.6 or 2 points. So, 2 for shooting plus 4 for walking are 6 points. Now, the soldier can react.
This could be a way to make the reaction more efficient. May be used the mind points, to make a "random" process, in order to apply the lucky factor.