Wax has memory. Not literally — it isn't thinking about anything — but it does remember the shape of its first burn, and it will try to repeat that shape every time after.
Which is why the first light matters more than any of the ones that follow.
What "tunneling" actually is
Blow a candle out after twenty minutes and only the wax directly around the wick has melted. The rest, right out to the edge of the jar, is still solid. Light it again tomorrow for another twenty minutes and the same small pool forms in the same small circle. Keep doing that and you'll dig a tunnel straight down the middle, leaving a thick wall of untouched wax around the outside that never melts at all — and eventually a flame sitting so low in its own well that it starts starving for oxygen and drowning in melted wax.
That untouched wax on the sides isn't decorative. It's fragrance you already paid for, going nowhere.
What to do instead
The first time you burn any candle, let it run until the melted pool reaches all the way to the edge of the jar — the full diameter, not just a circle in the middle. For a candle this size, that's usually somewhere between two and three hours, depending on the room. A draught slows it down. A closed, still room speeds it up.
Once that first full pool has formed, the candle has "learned" its shape, and it tends to burn evenly from then on.
One more thing, and this one's for every burn, not just the first: trim the wick to about 5mm before lighting. A long wick means a bigger flame, more soot, and wax that burns faster than it should.