It's not a 'likely possibility'. It is your opinion of course, and you're entitled to that, but some opinions are built upon much stronger foundations than others.
Everything we know about the cell towers in that area, the state of mobile phone technology in 2009, as well as polis disclosure; tells us that Claudia's mobile could not be "narrowed down to a much smaller area".
There's probably nothing more to say on this unless you can demonstrate otherwise.
Respectfully, there's plenty more to say. Not least of which is the fact that I used to work as an IT administrator maintaining computer servers and all related connectivity. I have no interest in becoming "verified" so I will nonetheless say this is just my opinion.
In 2009 LE in the UK was more than capable of using cell tower triangulation to narrow down the location of a cell phone. A cell phone in 2009 may have only made a full connection to one tower at a time (in this case the University tower) but it would be pinging other nearby towers to check for a better/stronger/lower latency signal. Those pings would be recorded and could be used to narrow down the likely location. This was perfectly possible with 2G mobile technology in 2009.
A cell tower may cover an approximately 9-mile radius, but even in 2009 a city such as York would have had many more than just one cell tower to cover the entire 9 miles. Cell towers overlap their signals to provide stronger, more even coverage with minimal dead spots. This was as true in 2009 as it is today--though there were certainly fewer towers in 2009 than there are today.
York city centre is only a short distance away from Heworth--it's virtual insanity to think the whole of a major tourist city would rely on a single cell tower in the suburbs. It's probable that even in 2009, there were at least half a dozen towers close enough that Claudia's phone potentially could have connected to them.
Had Claudia's phone been closer to a cell tower in the city centre than it was to the tower at the University, it likely would have connected to the tower in the city centre rather than the one at the University. That alone would give the police a strong hint that the phone was still in the exact Heworth/Melrosegate area where Claudia lived, worked and was expected to be.
The police have almost certainly announced that Claudia's phone connected to the University's cell tower because they believe it is important and suggestive information--that her phone was still within the vicinity of her home and workplace. They gain nothing by saying her phone DIDN'T connect to other cell towers close by. Nor do they gain anything--other than spooking a potential suspect--by announcing that they have or possibly could narrow the location down further.
The mere fact that Claudia's phone connected to the University tower, and not any of numerous others in the York area, is highly suggestive that her phone was much closer to that specific tower. Together with triangulation of pings from other towers, the location could potentially have been narrowed down to within a few blocks. Even in 2009.
This is all just my opinion built on crumbly foundations.