I have also run some calculations for early Steppe DNA appearances in Southern Europe (ATP3 in Northern Spain 3,300 BC and Croatian Vucedol 2,800 BC). These look related to each other, but not directly related to Bell Beaker, Corded Ware or Yamnaya.
ATP3's best fit comes out as 39% Central Anatolian Neolithic, 38% Bulgarian Steppe-like Chalcolithic and 23% Bulgarian other Chalcolithic.
Steppe-like Vucedol's best fit comes out as 33% ATP3, 24% Khvalynsk Q, 23% Central Anatolian Neolithic, 17% Cucuteni-Tripolye and 3% Ukraine early Chalcolithic.
My reading of this is that the origin looks most like East Balkan Suvorovo that branched off early up the Danube, with ATP3 venturing as far as Spain and pre-Vucedol staying in the Northern Balkans and mixing with Cucuteni.