They didn't settle in Russia. In fact Russian princes (knyaz) had to go to the Horde to obtain a license to rule. If we had a signigicant amount of Mongol admixture, the most common haplogroups in Mongolia - C and O wouldn't be present at such a low level - less than 1%. Another funny thing - the most "mongoloid" ethnic Russians are actually in the North which wasn't affected by the Mongols.