Summary:
In addition to the top collision box at 14px from the bottom, soul sand has additional collision boxes at 12px, 10px, 8px, 6px, 4px, and 2px from the bottom.

8, 6, and 4 snow layers have the same extra collision boxes (when applicable) while 7 snow layers has them every 4 pixels.

Steps to Reproduce:
1. Place soul sand or snow layers

2. If using soul sand, surround it 1 block above with another block (the soul sand will push the player out otherwise).

3. Stand on the soul sand.

4. TP the player down through the top collision box of the soul sand with the command

/tp ~ ~-0.01 ~

4. Repeat this command for each additional collision box.

Observed Results:
The player stops falling and stands inside the soul sand at heights of 0.75, 0.625, 0.5, 0.375, 0.25, 0.125 for each use of the command before eventually falling fully through the block. For 7 snow layers, they stop at 0.5, and 0.25. For 6 snow layers, they stop at 0.5, 0.375, 0.25, and 0.125. For 4 snow layers, they stop at 0.25, and 0.125.

Expected Results:
The player would fall completely through the block to match the behavior of other blocks, including other non-full blocks like honey blocks.

Notes:
This behavior was not observed in 1, 2, 3, or 5 snow layers.

For soul sand, this behavior was introduced in the full release 1.14.2, perhaps due to the fixing of MC-148677