One of the reasons you could be experiencing a slower time to retrieve the same data could be the communication and data processing overhead variation of using different polling methods.

You could check if this is the case by seeing which polling method the external tool is using to perform the gets.

On this page (Link), you can see an overview of different methods of polling data, and in the comparison section, you see that the main disadvantage of the GetNext method (i.e. retrieve cell by cell) is that it is slow.

When communicating with devices, we always try to use the methods that retrieve the most data per request (i.e. retrieving multiple rows at once).

When this results in scenarios where the device cannot send all the data of a single request in time, we sometimes have to tweak slightly the amount of cells/rows we retrieve or even going with a different polling method.

So in your case, I would try to increase the number of cells to achieve a point where you have some better performance without having issues in retrieving the data.