Fire is slightly larger than 1 block horizontally

 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).