2 block high nether portal can place you under nether portal

Entering a custom small nether portal that is only 2 blocks high and going in can cause you to be placed inside portal frame or under the portal often inside blocks.

To reproduce.

1. Create a nether portal of only 2x1 or 2x2. /Fill command is required
2. Enter the nether portal. you should be inside portal frame or under the portal.