I'm not sure about the maxRangeProbab though.. It may need to be lowered to be more effective..
I'm not entirely sure on this but this is what I've noticed,
I think the min/mid/max RangeProbab is the probability of a direct hit at that range,
so going off your modified ammo details above:
There is a 10% chance of a direct hit at min range(1m)
A 80% chance of a direct hit at mid range (200m)
And a 15% chance of a direct hit at max range (1500m)
Therefore increasing the min/mid/max RangeProbab number will increase the chance of a direct hit.
(i.e. A value of "RangeProbab=1.0;" will mean a 100% chance of a direct hit. Though I dont think this includes the variability caused by the "dispersion" value in the weapon config.)
I'm not sure if this is the way it works for rifle ammo, but I have noticed this with aircraft bombs.
A bomb example:
minRange=500; minRangeProbab=0.40;
midRange=1000; midRangeProbab=0.55;
maxRange=2500; maxRangeProbab=0.85;
If a tank is targeted and a bomb is dropped at 500 metres from the tank there is a 40% chance of a direct hit on the targeted tank.
If the bomb is dropped at 1000 metres from the tank then there is a 55% chance of a direct hit.
And if it is dropped at 2500 metres from the tank there is a 85% chance of a direct hit.
I could be entirely wrong on this, but this is how I've always interpreted min/mid/max RangeProbab values.
I hope this helps and I hope I'm right..