Excel 365 - Filtering is faster when formulas reference tables in a different file

Question

I have a file called "one.xlsb", in which there is a table called "t_formulas". That table is ~1000 rows by ~30 columns, and uses formulas to make calculations based on other tables, which contain data (these tables are called "t_data1", "t_data2", etc.).

For some reason, if these data tables are in the same file as "t_formulas", it takes ~30 seconds to apply any filter to "t_formulas".

So :

• I made a copy of "one.xlsb",

• I called the copy "two.xlsb",

• I changed all the references in "t_formulas", so that they referenced the data tables in "two.xlsb" instead of the original data tables.

  For instance, if the original formula looked like this: =t_data1[@ID]=1

  then I changed it to look like this: ='two.xlsb'!t_data1[@ID]=1

Suddenly, filtering "t_formulas" took less than a second instead of ~30 seconds.

To me, that's counterintuitive: it should be faster to reference data from the same file than data in a different file.

Does anyone know why?

Also, is it possible to make filtering just as fast without having to separate the data tables and the formulas table in two different files? It's a bit cumbersome to add 'two.xlsb' before every single reference…