Information

Minecraft version: 1.18.2
Modloader: Forge
Forge version: 40.1.80
Environment: Singleplayer

Mod name: Smaller Nether Portals (Forge)
Mod version: 1.9

Description

If the portal doesn't have 2 blocks underneath it, it won't open the portal. Vanilla portals will open but a 2x1 for example will need 2 blocks beneath the obsidian one to light.

Can you post a screenshot of what you mean exactly?

This bug is still present in the latest version for minecraft 1.21.3, but specifically for (skyblock style) using fire spread by lava to light the portal. I assume the original fix for this didn't take into account lighting portals without flint and steel (if it was fixed at all, i haven't checked) but to replicate, make the smallest portal, put some wood blocks next to the portal's entrance, and light them on fire indirectly so the fire spreads to the inside of the portal.