Nicksaurus will have to look into it, but in the source-code of Foreman I can see that he is using the formula mentioned in your link.
public float GetRate(Resource resource)
{
return (this.MiningPower - resource.Hardness) * this.Speed / resource.Time;
}

So either the base values are wrong, or ...

First of all, wonderful tool!

Just one thing I cannot understand. An Electric Mining Drill drills Iron Ore at a rate of 0.5/s.
Why does Foreman tell me I need 4 Electric Mining Drills for a total Iron Ore rate of 1/s? I would say I only need two.

Good to hear you have found a fix already.
Just to be complete, I ran into the same problem on a super simple track layout:

http://i.imgur.com/ZO8MNYh.jpg

Train will not path to the westbound station. But after I manually drive across the red line, it will.
Even after removing the top portion of ...