The 1.5x delay is just a compromise, because we can predict which callback is fired first. I could sea both cases during my tests. 
The desired value is 1x. If reading course first, we have 0.5 x delay, else we have 2.5 x delay. 
Then the drift correction starts to work and meld 0.5 x back to 1 x for the write case and 2 x for the read case.