It may not be the sexiest position in a batting order, but it is the sixiest. And over the years Australia have had some jaw-droppingly sixy Test batsmen - Steve Waugh, Allan Border, Ricky Ponting and Doug Walters to name a few. But Australia currently find themselves frustrated, unable to break a six-drought that grows with every Test. Australia, you see, have a headache, and they've had it for more than two years.

Whether Nic Maddinson is the man to break this drought remains an unanswered question. He struggled badly on debut in Adelaide, and again in his next Test in Brisbane. On day four at the MCG he seemed in the mood, but was then bowled by Yasir Shah for 22. Maddinson's innings was neither one thing nor the other, neither failure nor success. His 55 deliveries at the crease did little to confirm or annul his Test future.

And so Australia's headache continues.

Number six is a deceptively important position, and one that requires versatility. A good Test No.6 is a buttress in case of a top-order collapse, and needs to bat well with the tail. But if the top order has built a big score, he should also be capable of quick runs to capitalise on that platform. He is often the newest batsman in the side, sometimes a veteran shuffling down later in his career, at other times an allrounder.

For Australia right now, an allrounder has the greatest six appeal - they just can't find one. During this Test, bowling coach David Saker said Australia were "desperate" to find a fifth bowler who could ease the workload on the fast men. Desperation does not necessarily equal success. Mitchell Marsh has been tried, Hilton Cartwright could be next, Moises Henriques could even be considered down the track.

Since Marsh made his Test debut against Pakistan in the UAE in October, 2014, No.6 has been a problem for Australia. The following figures - batting average, number of centuries and number half-centuries for each position in Australia's top six since Marsh made his debut - are revealing:

Averages for top six since Mitchell Marsh's debut
Position Average Fifties Hundreds
 Openers  48.49  24  15
 No. 3  50.78  10  9
 No. 4  58.67  7  10
 No. 5  54.42  9  6
 No. 6  21.75  5  0

Marsh was No.6 for the vast majority of those innings, and his lack of batting output eventually led to his axing after the first Test of this summer. Callum Ferguson was then tried and discarded, a one-Test stand that satisfied neither party, and Maddinson replaced him. Both Ferguson and Maddinson meant a return to Australia's old formula of six batsmen and four bowlers, which worked when those bowlers included Shane Warne and Glenn McGrath.

There are those who point to Steve Waugh as an example of why Australia should have persisted with Marsh as an allrounder. In 19 Tests, Marsh has made 626 runs at 23.18 and taken 29 wickets at 37.27. Waugh's output after the first 19 Tests of his career was only slightly better: 689 runs at 27.56 and 29 wickets at 33.75.

But this comparison ignores a couple of critical factors. Waugh's breakthrough as a Test batsman did not come simply from staying in the team and gaining Test experience. He made serious Test runs - including his maiden century - only after going away and dominating at first-class level. Specifically, Waugh piled up mountains of county runs for Somerset in 1987 and 1988, and scored eight first-class hundreds in those seasons, averaging 78.76. Marsh has done nothing like that.

And when Waugh was first selected for Tests, he was averaging 43.21 as a first-class batsmen - Marsh was averaging 28.51. This is not meant to belittle Marsh - who is a fine player with all-round potential - but rather to show that expecting him to blossom as a Test No.6 was always a tall order. In fact, the uncapped Cartwright's first-class record - two hundreds and an average of 44.50 - is much closer to Waugh's pre-Test numbers.

There is a chance Cartwright could be considered for a Test debut at the SCG next week, given the workload for Australia's fast bowlers over the past two Tests, which would squeeze Maddinson out. But of course, the whole selection philosophy could change for the upcoming tour of India, where two spinners will likely play - perhaps even a spinning allrounder - and Shaun Marsh will also come under consideration.

And it should be noted that No.6 is far from Australia's only issue in the lower middle order. During the same period - October 2014 to now - Australia's Test No.7s have produced no centuries, five fifties, and averaged 21.66. Matthew Wade, brought in at the same time as Maddinson with the aim of shoring up the batting order, is yet to reach double figures in a Test innings this summer.

After Maddinson fell for 22 and Wade made 9 in the first innings in Melbourne, the captain Steven Smith said that Maddinson "looked pretty good" and Wade was "in a good headspace". But it's patently obvious that Australia remain at sixes and sevens with their sixes and sevens. It's the headache that just won't go away.

Brydon Coverdale is an assistant editor at ESPNcricinfo. @brydoncoverdale