Data Points Regarding Bell Beaker Origins

Razib Khan notes that the Yamnaya (or at least the Eastern Yamnaya for whom we have ancient Y-DNA samples, it is plausible that Western Yamnaya might have a clad of Y-DNA R1b closer to the Bell Beaker Indo-Europeans) cannot be the directly ancestral population to either the Corded Ware culture, or the people with steppe ancestry within the Bell Beaker culture, the two main archaeological cultures that brought the Indo-European languages to Europe. 

Instead, when the Yamnaya culture collapsed, Y-DNA suggests that some of its men (at least in the East) fled to Central Asia, and a minority were integrated into Indo-Iranian society. Most of their men were probably slaughtered or died from other conditions that precipitated their collapse and replacement.

"Matt" commenting at the same post, provides a link to a March 2021 talk by David W. Anthony (author of "The Horse, Wheel, and Language") comparing various autosomal ancient DNA samples in a PCA chart which Matt extracted from the presentation and annotated. Matt carefully provides a chart with and without his contributions to clearly attribute with comments are his, but I will include only the one he has marked up below.

This chart, labels notwithstanding, doesn't have any true Bell Beaker individuals shown, only members of the Unetice culture (a probably Indo-European culture ca. 2300 BCE to 1800 BCE in Central Europe including Southern and Central Germany, Austria, Czechia, Slovakia, parts of Poland, and Western Ukraine whose link to Corded Ware or Bell Beaker culture is unclear), and the Corded Ware culture. 

But the chart does suggest that Yamnaya people from Moldova, Hungary and Bulgaria (and less clearly culturally identified people from copper age Bulgaria and from Romania), who show an admixture pull towards the Neolithic farmer cultures of the Central and Eastern Europe, are a close genetic match for the subsequent Corded Ware culture and Unetice culture people. 

And, while the respective cultures were very distinct in Y-DNA (three of the ancient Unetice Y-DNA samples are I2 while one is R1b, those Y-DNA haplogroups plus a predominance of R1a are found in Corded Ware, and Bell Beaker is predominantly R1b), the autosomal DNA of steppe migrants to Europe was quite similar.

Thus, if you are looking for a launching point for the Bell Beaker culture, Southeast and Central Europe is a very plausible place to look.

Also, the original Bell Beaker culture in Iberia, according to ancient DNA, was probably not a product of steppe people. Instead, as it expanded out of Iberia, this culture was adopted by steppe migrants in Western Europe via central Europe, perhaps, in part, adopting some of the culture of their local wives.

The map below from Wikipedia places several of the cultures. The Neolithic farmer Globular Amphora culture (ca. 3400 BCE to 2800 BCE), immediately preceded the Corded Ware culture.

This map from Wikipedia places the Neolithic farmer Tripolye culture (ca. 5500 BCE to 2750 BCE) to the South of the Globular Amphora culture.