I’ll update this with some pics in a bit.
But the layout:
Deco gravel - X
Bonus block -O
OXXXOXXXOXXXO
XXXXXXXXXXXXX
XXXXXXXXXXXXX
OXXXOXXXOXXXO
So N/S 3 spaces between bonus block, and E/W 2 spaces (can be the other way around, but as long as it’s 3 one way and 2 the other)
The lava is channeled underneath.
Row 1 and 3 between the bonus blocks has a slope chiselled on the underside and lava filled in there.
Borrowed heavily from here:
The ‘broken’ lava channels work fine for combustion, but the kindling requires continuous channels, I thought I ended up just doing a continuous channel for both, but apparently not!
This is the underside of combustion:
For kindling make the lava channels continuous, and use the appropriate bonus blocks of course.
If you add a couple of lava spots in the corners (still underneath) you will have the same percentages on every deco gravel block.