I have read a lot of concerns and hoped to find an answer as I too have some of the same concerns. I finally found this.. Hope it helps everyone else…..
Federal law does not regulate the order that banks post checks to your account, but some state laws might. Bank computer systems may be designed to process checks randomly, from the largest to the smallest check amount, or based on some other method.
Some banks post the largest checks before the smallest checks assuming that larger checks are the most important payments being made by the customer, for items such as mortgage or rent payments, or auto loans. You may want to ask your bank which method it uses to post checks.