Mini DSP HT & REW Impulse response - acoustical reference. Please help

[Klimmzugernie]

Hello dear members,
I’m new here and already have a question about impulse measurement with an acoustic reference.

My name is Philipp, I’m 41 years old, and I’ve just completed my 3-way active project. I’m actually quite familiar with REW, but I’m struggling with the topic of time alignment measurement using an acoustic reference.
The measurements sometimes show a deviation of 0.1 to 0.05 ms. Is that normal, or am I doing something wrong?

 

[dcibel]

Make sure the acoustic reference is somewhat near the mic, of reasonable volume so it's well captured by the mic, and a driver with high frequency output, ie a tweeter. If there's significant reflections in the reference recording, REW may have a hard time picking out the fundamental impulse peak from a reflection. Mind you, 0.1 and 0.05ms is 17-34mm of physical distance, so not likely a room reflection.