I found a video for 1100D modification on youtube:
https://www.youtube.com/watch?v=gQyT0XoryW4
Unfortunately I dont understand the language. But what I can see that after the filter assembly is removed, there is a clear glass on the sensor frame: see the video at about 11:33. Somewhere I read it is a protective glass. The guy in the video is saying something about the glass, but cant understand it
As per the diagram given earlier, The LPF1 should be the first filter facing the lens? If yes, then it will be part of the filter assembly.
I my case, I just removed the filter assembly completely, which makes me believe that there is no filter left now.