Tank aggression is just a myth. Im telling you that and im 100% confident that im right. Snakes are a bit smarter than most give them credit for and they can certainly tell the difference between a rat and your hand.
Also when you are transferring them to and from a seperate feeding tub you have a better chance of being bit. The snake just finishes eating and is still in feeding mode so when you go to grab him he may think its another rat.
EDIT: im am only speaking from experience with my bps. I know that other species, retics come to mind lol, can be very cage aggressive. Like you slide out the tub and they come flying out ready to pound the first living thing they see lol.