I'm really struggling to think of a way of answering this without simply noting that it really depends on what the decision was about, and when.

In general terms big decisions were settled by the Politburo before being transmitted for approval etc. down the line. That being said a lot of the time there wasn't really a heap of discussion about the pros and cons of a decision in the Politburo - the decision would essentially be sorted out prior to the meeting, probably informally by phoning/meeting the key people and sorting out what was going to happen at the meeting ahead of time. That being said some decisions probably were debated to some extent, or the details of how a new policy would be implemented could be thrashed out to some extent.

A lot of decision making was also essentially done by ad hoc or formal committees. For example a lot of the Soviet decision making around what would become the Afghan War was done by a 'special commission' featuring Yuri Andropov, Dmitri Ustinov and Boris Ponomarev. In a sense this followed from the older practice of someone in the leadership being directed to sort out a specific problem and report on it - for example Lazar Kaganovich being tasked to sort out why so many tires were defective (IIRC this was during the 1st Five Year Plan... might have been the second?).

But another factor to consider is the prevailing policy/leadership style of the time. So under Khrushchev you could expect Khrushchev to mix things up a bit. Like using 'lower' party bodies to influence decisions made by the 'upper' body Politburo (Khrushchev marshalled support in the wider party to stave off opponents in the late 1950s for example - the Anti-Party Group IIRC). Or Khrushchev's tendency to intervene personally in decision making and the running of certain projects, much like Stalin before him. Khrushchev was less inclined to consult with his colleagues on decisions than they would have liked... so they eventually kicked him out.

Under Brezhnev you're looking at a less interventionist leader, and political leadership generally. For example the details of the running of the economy was less driven by the Brezhnev-era Politburo compared to earlier eras, and you could expact state organs like Gosplan or he industrial ministries to have more a free hand in those sorts of areas. In line with this was a stated policy of 'trust in cadres' and generally respecting 'experts'. Brezhnev seems to have been a lot less interventionist as a leader, so if you look back to the Afghanistan commission above, you'll note this somewhat important group didn't include Brezhnev as a member and he doesn't seem to have had much direct input on policy in that area. Part of this was Brezhnev grew quite old and decrepit in office, but the lack of interventionism also applied to the earlier part of his era and probably reflects the rejection of Khrushchev's approach (or fear of what would happen if it were replicated). Under Andropov and Chernenko you get a similar process to the Brezhnev era, again partially influenced by both being aged and infirm at the time.

Under Gorbachev it gets even more complicated as he introduces new governing bodies and offices as part of his later political reforms. From 1985-1986 approximately he stuck with the existing system, albeit with more dynamism from Gorbachev and some other people who had been moved up the ranks. The later period gets confused enough that the newly created leadership positions effectively contested the Politburo's ability to make decisions. So for example the clashes in the early 1990s between Boris Yeltsin (first in the Congress of People's Deputies, then as President of the RSFSR) and the leadership.

Now as for decisions affected specific regions, industrial sectors etc... again it really depends on when and what exactly it was. Some of the ministries were quite powerful and during some periods were allowed more autonomy. The Ukrainian scenario you mention might have been resolved by the Ukrainian party structure, but that decision may have been influenced by the assumed or actual response from Moscow if they had done the 'wrong' thing.