Actually, 123.5usec is almost exactly twice of 1/16384Hz.
Because of the loop, we have 1/16384Hz delay. I wonder where we do have the delay.
In order to understand the behaviour of the system can I ask you to test the following things?
1) What are the delay without IOPs with fsampl of 16k, 32k, 64k?
2) What are the delay with IOP with fsampl of 32k, 64k?
TF agreed well with 2-time feCoeff4x and CDS time delay was -123.5 usec.