I am a Hindu Nationalist but not a Hindu chauvinist. If they were centered in Yamnaya region (oldest IE culture near Astrakhan as Seroglazovo, 7000 BCE), the question will be from where they might have come there? Both in Avesta and in RigVeda, there are indications that they came from a place where the dawn lasted one month and the night for two months. Such a place could only be in Western Siberia within the Arctic Circle. Avesta talks of a flood by snow when Ahur Mazda asked Yima to make an enclosure and keep his people there. It could have been the ice-age which made the PIE migrate to warmer regions. Even in other places (Denmark for example), ice-age made people to seek refuge in warmer southern refugias. They moved north again after the snows melted.