I only found this interaction because I wanted to save time salvaging multiple debris fields. I was in a system with multiple pirate fleets, and I just stayed in one location and took the fights as they came.
At the end of the battles, I sat amid a large, dense debris field. And then I activated my salvage ability, only to discover that my salvage opportunity was high risk, low reward, completely opposite my expectations. After taking crew and machinery losses, I was shocked to discover that my salvage got progressively BETTER with each successive attempt.
What probably happened: I fought the strongest fleets first, and then killed off the weaker stragglers at the end. The newest salvage got stacked on "top" and so the small fleet salvage got stuck at the top of the stack, while the lucrative salvage at the bottom was hidden below.
What I expected to happen as a player: All debris fields would combine into one, leading to a mega salvage opportunity.
What I did not like about this interaction: I had to suffer losses to get to the good salvage, with no way to "ignore" the top stack.
If the debris fields combining is impossible, my minimum expectation would be for salvage stacks to reorder from best to worst, not vice versa.