A slanted nest box can cause the eggs to roll the direction of the slant, I've know some henhouses to have it set up so the eggs roll out the back of the nest box and fetching them is a snap. Commercial eggs production doesn't use nest boxes they just have a slanted bottom on the cage and the egg rolls down the slant onto a platform or conveyor where they are gathered and moved to the next stop, the cleaning station.
Natalie is right about the hens using the same nests and rebuilding it each time, and occasionally an egg gets broke when 2 or more chickens are in the same nest box at the same time. I've had as many as 3 broody hens trying to set in the same next box at the same time, the result if that not all of the eggs are covered all the time and getting any to hatch is more luck than anything else.
To solve the broken egg problem as much as possible:
Use large Nest boxes 16X16X16 works for large as well as small and medium chickens. Keep the nesting materials in the nest box. I usually have to put more hay or wood shavings (I use both) in the next boxes each week. The nesting materials act as a cushion but 2 hens trying to use the same nest box at the same time can be problematic. Chickens like to use each others nests and it is not unusual to have a flock of 2 dozen layers and only find eggs in 3 of the boxes. Also don't be afraid to let them build nests on the floor, this will take some of the stress of the favorite nest boxes and some hens prefer to lay their eggs on the floor.
Most of the eggs are laid between 6 and 2 pm so timing the collecting of the eggs can make a difference so that the eggs don't build up too much. I try to collect mine around noon as the majority of the laying for the day is over by then. Check every nestbox, look or other places they might like too lay and check under the setting hens. Usually a setting hen can be picked up, eggs removed, and sat back down again without making to big of a squawk.