Imagine if, this summer, one of the key players in a National League promotion-winning team suddenly became available. He was experienced - "a real stalwart", according to his manager - and just happened to play in a position that was a problem for Carlisle United last season.

You'd expect the Blues to take a look, at the very least.

The gap between the fourth and fifth tiers in England isn't great, we know that now. The way Richie Bennett has stepped up from Barrow highlights this; so does the trend for promoted teams to survive, or better, in their first season in League Two.

A player with personal momentum from what used to be called the Conference can be a more attractive option than a time-server from higher up. So far, Bennett looks hungry and capable. "He's adapting very well," Keith Curle said. It is easy to see why United's manager pursued him.

Attack was certainly one department Carlisle had to address this summer, having been left with one striker after the end of 2016/17. But nothing needed attention quite like the other end of the park.

United's defensive record was not that of a promotion team and one has to wonder, now that Mark Ellis is back in the fold, whether it is a case of not knowing what you've got 'til it's gone.

Big conclusions can hold for a few weeks yet, considering the campaign is 270 minutes old (plus 30 of extra-time). Ellis, though, has certainly looked solid since regaining his place. The first signs of a useful centre-half partnership with Tom Parkes are there, and two starts have yielded two wins.

At the very least, there is a case for Ellis to continue, just as there may be grounds for asking why it took quite so long.

The obvious answer is that United were in no position to recall the 28-year-old once they had loaned him to Forest Green Rovers in January. That transfer was sanctioned partly to free up wages so the squad could be improved elsewhere.

It was, in this respect, a pragmatic move, rather than simply casting a player into the wilderness. But still - you don't part with someone you really want to keep unless it is a last resort, or your hand is forced. It is not as if Ellis had been in consistent favour throughout the first half of the season, when Carlisle's results were strong but their goals-against total was showing as a warning symptom.

So they were not exactly on their knees, begging him to stay. And so, while United tanked in the early weeks of the new year, needing a late rally to salvage a play-off place, Ellis established himself at the New Lawn, where Mark Cooper's team won at Wembley to rise into League Two.

He got better the more he played, said Cooper last week, and now that he has landed back in United's lap it is difficult to make a case against Ellis getting a fair chance to rebuild his first-team status at Brunton Park.

After all, others in his position have been given plenty of opportunities without tightening United's back line - and when one looks at the defensive statistics at the club it would seem logical to expect the man from Devon to provide at least some improvement here.

So far in a United shirt, Ellis has made 50 appearances. Those games have seen 14 clean-sheets and the conceding of 62 goals. His clean-sheet ratio is 0.28, while Carlisle concede on average 1.24 goals when Ellis plays.

Without context, those figures may seem unremarkable. But they are still the best of any defender who has been at the club since Ellis joined in October 2015.

And so, while they might only tell a fraction of the story, should they also be dismissed? Surely it is better, if United are serious about improving their security, and preventing goals landing in their net quite as often as guano has been hitting the seats in the Pioneer Stand, to fully examine any potential advantage, no matter how small.

After Ellis came in during the 2015/16 season, Carlisle became better defensively but, slowly, more sterile at the other end. The arrival of Nicky Adams and others the following summer duly improved them in an attacking sense.

A side at United's level is rarely stable for long but, broadly speaking, improving the base from which Adams and company can work is the challenge 12 months on. Without a great deal of cover, or much money to go off and find alternatives, a player who ended last season in good form, has promotion experience at Carlisle's level and did not do a great deal wrong in his longer runs in the team has to be worth a reasonable chance of firming those foundations.

'Head it and kick it," is Ellis' Twitter description of his style, and already in 2017/18 we have seen that there are times in League Two when that is exactly what is needed. He is, on the current evidence, as good as anything United have in that department and right now it is hard to see why Curle would look too far elsewhere.