It should come as no surprise that Bristol City's recent improved defensive record has coincided with long-overdue consistency of selection.

Robins boss Gary Johnson has seldom been able to field an unchanged back four or three this season, such has been the extent of the injuries and illnesses which have served to deplete his squad at one time or another.

Already denied the services of injured centre-back Jamie McCombe and utility player Brian Wilson for the remainder of the campaign, City's manager had to perform a further re-jig when first-choice left-back Jamie McAllister sustained a calf strain in a Championship fixture against Watford at Vicarage Road on February 9.

Absenteeism on such a scale forced Johnson's hand and in came Lewin Nyatanga and Liam Fontaine to partner City stalwarts Bradley Orr and Louis Carey in a four-man defensive unit not previously tried this season.

When things went badly wrong against Sheffield United, who inflicted a painful 2-0 defeat at Bramall Lane, Johnson decided to carry out some fine tuning. This involved Nyatanga and Fontaine exchanging positions, a switch which yielded immediate dividends, City earning a 1-1 draw and posting a much-improved performance against Leicester to stop the rot.

That improvement was maintained as automatic promotion contenders West Bromwich Albion were beaten 2-1 in front of the TV cameras at Ashton Gate, after which the Robins dug deep to carve out a goalless draw against Ipswich at Portman Road, in the process registering what was only their second clean sheet in 16 outings. Although City's improved goals against record – two in three games as opposed to 12 in the previous five – cannot be attributed entirely to the positional switch, the defence has certainly looked more assured since Nyatanga moved inside to partner Carey in the centre, allowing Fontaine to adopt the left-back role hitherto reserved for McAllister.

"Our back four has looked better as a unit," confirmed Johnson, whose revamped team has taken five points from three games to dispel fears of a relegation dogfight.

"All four of those players are very committed defenders, who have done a good job for us this season. But it took that extra little tweak for it to come together as we wanted.

"Not only are they working well together as a unit, they are also picking up their respective markers and getting tight when the ball comes into our 18 yard box. That has been a big part of our recent improvement."

Uncomfortable on occasions when exposed to an especially quick right winger, Nyatanga has looked more at home at the heart of defence where his aerial ability and physical strength have served him well, while the ease with which Fontaine has adapted to his new role suggests he has been playing on the left side of defence for years.

"It's a matter of playing to your strengths and those two have done very well since switching places," said Johnson. "Lewin appears far more assured in the middle of the back four and, if you look closely, you will see that he is first to the ball most of the time.

"As for Liam, we feel he is better equipped to get forward and set-up attacks. We like our full-backs to push on and Liam has that in his game, while Lewin tends to stop at the halfway line.

"Liam is also that little bit quicker and can get up and down the pitch without too many problems."

As a consequence, City have been able to defend higher up the field, a factor which has helped relieve the pressure on Dean Gerken's goal.

Under almost constant pressure in games against Cardiff, Watford and Sheffield United, the Robins were guilty of dropping too deep, a trait which has contributed in no small part to the worrying series of last-gasp goals conceded this term.

Although City rode their luck on occasions in the first half against Leicester, they adopted a higher defensive line after the break and dominated thereafter. A similar platform enabled them to wrest the game from West Brom and come from behind to win 2-1.

Indeed, it was noticeable that, after City scored twice in four minutes early in the second half, Albion hardly threatened Gerken's goal.

Johnson will expect his team to defend a similarly high line when Doncaster Rovers visit Ashton Gate tomorrow. No matter the outcome of that game, it seems Orr, Carey, Nyatanga and Fontaine will, injury and suspension permitting, be allowed to work together for a good while yet.

McAllister is recovering only slowly from the calf strain that has already caused him to miss three matches and it could be another few weeks before he is considered sufficiently fit to return to Championship action.

Even then, his return to the starting line-up will not be guaranteed should the back four steer clear of injury and Fontaine and Nyatanga continue to progress as they are.

"That is why you need a big squad in this league," argues Johnson.

"We will be a bit thin on the ground if we lose any more defenders, but we've already lost McCombe and McAllister and still been able to field a strong back four. It's something we would have struggled to do last season."