That is a possibility indeed, as Scrap Items isn't rewarding with a static number, but with a range of values (e.g. between 1 and 50 items). So you should be getting x4 more resources on average, but the minimum value x4 may still be lower than maximum value from the previous level.
However, I'll certainly run some tests to make sure this is the case (will post again if it's not!).