You need to increase the number of simulations, akanaki. And maybe dnarag1m needs to do that as well...
With 5000 simulations your setup also has the same chance of losing lots of crossbows: 149R 1S 20C 58A !
The reason for those maximum losses is the rare occasion where the Dark High Priest isn't killed in battle round 3, and gets one extra charge.
When optimising the number of units, always check if you can get the maximum number of rounds of fighting down one extra step.
That might have quite a significance when attacking leaders with splash damage, and especially with the High Dark Priest, who has last strike.
In my guide for the Old Friends, I have this setup for that camp (number 6 in my guide):
With this setup the Dark High Priest is always killed in round 3.
And since there is a very small risk of one soldier dying, I have used two of them, to ensure no cavalry ever dies.