Puzzle solved by Ian Lee. Thank you Ian.
The issue was that in the fonts in my computer, lowercase "L" and number "1" appear exactly the same. So 1000l (l for Long) reads as 10001.
So my frequency numbers are all too small by a factor of 10.
Here is the corrected graph and it explains why the slope of the filter is not noticeable on the audio since we are introducing about 1dB of impact between 500Hz and 2400Hz when using the slope of the filter.
Now the theory matches the practice..hihi
It also means that the first IF filter is (in my case) around 7000Hz out of alignment with my 2nd IF filter, as mentioned before.
Please note that Ian has released a video of the 1st If shift. See??
I will correct and re-upload the test sketch as well.
All the best,
73, John (VK2ETA)
