>>518856405
The number of mosques is weakly correlated to the number of Muslims since the size of mosques varies dramatically. Same with churches. Small towns tend to have small churches/mosques. While big cities tend to have big churches/mosques.
In the case of church, certain denominations tend to build megachurches that look more like football stadiums on Sunday. While others have 50 congregants or less.
The places where Muslims live in Russia tend to be more rural.