Wrong. This is how many hens end up getting killed by the toms. Hens on their nests need to be protected from the toms. The hens typically do not fully cooperate when on their nests and the tom in his excitement can and does often slip off and in the process rips the hens side wide open with his spurs.
When mating under proper circumstances the hen will lie down in front of the tom and will cooperate as he gets up and stands on her back. Once the hen starts sitting on her egg, a tom with only one hen available will seek her out and because she is already lying down will proceed with the unwanted (by the hen) mating whether or not she cooperates.