That's where we differ... I see Beakers as Unetice-like men + local cuties.
L11 (more probably L11+) settled in Bohemia/Poland. Some of then remained there and over time developed into the Unetice culture.
Those L11+ people thought in terms of "clan" - the extended family, something like the Roman gens. As the organization was strongly patriarchal, each clan probably had a distinct territory of their own, as well as a distinct forefather of their own. So I guess U106 clans and P312 clans, though neighbors of common extraction, originally sharing the same language, kept themselves to themselves.
U106 clans moved north little by little, mixed with CW first, then with I1 people their advance had pushed ahead. This resulted in Proto-Germanic, i.e PIE altered by local phonological traits and lexical additions.
P312 moved west, mixing with LBK-type people. I think L21 clans moved early, and retained their PIE kw- sound. There must have been a series of raids towards the southwest first, which would explain the low, but fairly homogeneous distribution of L21 all over today's France (Brittany not included) and Iberia (notably the north-west). Maybe DF27 followed - simultaneously or shortly afterwards. They kept in touch with the people they had left behind, and traded with them. Along those trading routes the beaker package spread quickly. The (surviving) natives may have taken advantage of the new opportunities, hence the Beaker samples identified as "southwestern" in southern Germany. Then, from what is now the Rhineland or Benelux, L21 massively and aggressively moved to Britain, bringing along both the 'steppe' and 'beaker' packages.
Those P312+ clans were violent, but not all equally numerous. They mixed abundantly with local women. The y-dna was altered, the autosomal mix was far less impacted. The Lusitanians retained their Proto-Italo-Cletic language. The Ligures mixed theirs with local non-IE languages. The Basques lost theirs.
Meanwhile, U152 stayed north of the Alps, mixing with locals in just the same way. It's easy enough to imagine an east-west linguistic gradient, with the west shifting away from the original as admixture intensified. Somewhere in Austria, tribes kept their kw- sound. In due time, they'd move to Italy and speak Latin. Further to the west, with more local admixture, the P shift occurred, probably because the local people couldn't manage the kw- (and because that kw- seems to have been fairly unstable anyway). The ancestors of the Osco-Umbrians may have lived there, with a language akin to latin, but affected by the sound shift. Further west: the P Celts that would later descend on Gaul and Northern Italy.
These are convictions, not certainties. No-one need agree. I know Ygorcs, for one, will contend that my glottochronology doesn't hold water. Well... alternative scenarios are most welcome. Feel free to criticize and amend.