So, true story, I was messing around with a Yuoki Industries map idea when, trying to figure out how to automate raw wood production, I came a cross your wooden fence. It costs 4 planks of wood to make, total fuel output equaling 8MJ, and I can craft it into said wooden fence, no muss, no fuss, with a total fuel output equaling 24MJ.

This renders any solid fuel set-up via carbon (which is far more precious than wood) obsolete, considering you can start making these things right out of the gate, and can mindlessly be automated just as early. Considering how easy it is to grow massive forests via your sapling recipe, I would change the recipe to 4 raw woods (instead of planks) and set the fuel cost to 16 (to mirror the cost of the logs); Or, if you're insistent on keeping the recipe using planks, simply reduce the fuel cost to 8MJ, to mirror the fuel cost of the 4 planks.

As with all my suggestions, the choice is up to you.