Group by ratio, not by asset
Switching aspect ratio mid-batch means re-checking composition each time, and composition problems are ratio-specific. Doing all the 16:9 assets together lets you fix a framing issue once.
Wide ratios also need a larger rejection allowance than square ones, so grouping makes the budget more accurate as well.
Wall time is usually the binding constraint
For a marketing set the money is often trivial and the elapsed time is not. A thousand generations at twelve seconds each is over three hours serially, and concurrency is what fixes it.
Check your provider’s concurrency limit before planning around a number you cannot actually run.