Players with increased step height can fall by 1 block or more even when they are sneaking.

Reproduction steps:

1. Increase player step height, for example with the following command:

   /attribute @s minecraft:generic.step_height base set 10 

1. Try to sneak while moving on top of a block.
2. Notice that you can fall by 1 block or more. The larger the step height, the more it is possible to fall.

This is likely due to the use of this.maxUpStep() inside of Player#maybeBackOffFromEdge and Player#isAboveGround, which causes the checks to scale with the step height.