Steps to reproduce

1. Place a netherrack block in the air.
2. Light a fire on top.
3. Place a dark block besides the fire (dark for better contrast).
4. Look from below.

Observed results

See image attached. You can see a faint line of the bottom of the fire texture.
If you look carefully at the fire without the block on the side, you can see a gap where the opposing side's fire texture is visible.

Expected results

No gap. Fire textures are contained exactly within the block (horizontally).