Applying a Filter within a UDF without Affecting UDF's which Look at Same Data Set/Range

I have a UDF in sheet 2 which does calculations based on data in sheet 1.

I have written a new UDF in sheet 3 which also looks at data in sheet 1. The issue I have is that the UDF in sheet 3 applies a filter to the data in sheet 1 which then causes in to essentially step in to the UDF's in sheet 2 as the filter has been applied to the same data set used in both functions.

If I change the calculation option to 'manual' and step through the function in sheet 3, it works as it should however the above problem is causing it to produce erroneous results when the calc option is set to automatic (which is the option I need it to be on).

Is there any way around this other than not using the filter within the function?

Thanks in advance