16GB xavier developer kit with 32GB module difference

I use 16GB xavier developer kit and 32GB module flash the same system, Test the 45 channel video demo using Deepstream4.0, The results show a 2GB difference in RAM usage.Why is it different?
The purpose of this test is for one of our clients to use 32GB Xavier Module, our own board, to test their own program, the memory consumption is up to 19GB, they said the normal should be 12GB.
The following picture shows the situation of our test demo.

Would like to confirm the release version. So you are on r32.3.1(JetPack 4.3) + DS4.0.2. is it correct?

r32.2 (jetpack4.2.1)