This is what I don't understand:

"ROWS_PER_BATCH should approximately the same as the actual number of rows"

It means that all the rows would be in the same batch. And we are good if we give a hint of batch size rather than row size.

The word 'ROWS_PER_BATCH' gives an impression that these many rows will be sent to sql server per batch instead of sending all the rows at the same time. But the sentence contradicts this:

""ROWS_PER_BATCH should approximately the same as the actual number of rows"