Content Query Web Part - number of items in a column

Hello:

I am having hard time predicting/defining no: of items in a column. I set the no: of columns to be 3 and total number of query results are 50. First column displays 30, second 15 and last 5. There seems to be no deterministic logic behind how many items are displayed in a column. If I change the no: of columns to 2, first column displays 40 and second 10.

Is there a way to adjust the no: of items displayed in a column to be equal across columns? Is it possible natively by adjusting a parameter?

Thanks!