So The audio fade in/out I think needs a little adjusting. I have it on a song that suddenly starts and I tried to use the fade in to gradually raise it in but it doesn’t seem to follow it linearly like it depicts. Basically it seems to rush it in the last few seconds rather than a full build up. With my volume halfway (Fairly loud with the song going normally) it takes about here (Fade in is set to 5 seconds currently) for any audio to seem to play at all. Maybe a “starting volume” addition to the fade in would help a little. Maybe it’s just me but it just feels like it doesn’t fade in as well as it could. Even at higher amounts of time like 10 and 15 it seems more slow at the start then rushed at the end, and at those times I miss a large chunk of the song. 
Hi,
I’m not pretty sure I understood correctly, but if so:
I always use the volume filter, combined with a keyframe.
HTH
The dBFS changes linearly, which means the volume changes non-linearly (log) due to human perception of loudness. This is very common practice in multimedia applications. If you do not like it then keyframe the volume to your own liking as I am not going to change this.