TL;DR: at the bottom.
Got some more info with the help of Bonesy, one of the modders at D2RModding. 
I’ll be honest that I’m out of my element when it comes to server functions and stuff like that, but I’ll try to explain to the best of my limited knowledge of what’s going on with Strafe.
The reason why the AR% isn’t working is because the backend/hardcode of the “srvdofunc” that Strafe uses in skills.txt isn’t properly setup, so the “tohit” (baseline AR%) and “tohitlvl” (AR% per level) of Strafe doesn’t have any effect at all.
What is “srvdofunc”? I’m not really sure myself so I’ll just copy it from the Phrozen Keep:
srvdofunc : Server finishing function, this controls the server side function executed when the starting function finishes executing, it might either be called repeatedly as long as the mouse button remains down, or it may be called periodically (for skills like paladin auras and blade shield).
So this requires a backend fix of “srvdofunc” 12 (the one that Strafe uses) for the AR% of Strafe to work, at least from what I understand.
I tested this by changing the “srvdofunc” of Strafe from 12 to 1 (the same one used by normal attack) in skills.txt and the AR% worked, I changed it back to 12 and tested it again and the AR% had no effect again.
I also tested if it was an issue with the missile by changing the “srvmissilea” of Strafe from “strafearrow” to “multipleshotarrow” and the AR% still didn’t work, so it seems unlikely for that to be the issue.
TL;DR: “srvdofunc” 12 (the one Strafe uses) needs a backend fix to make the AR% work, currently the AR% has no effect.
I made a new bug report here since it’s a separate issue from the Strafe damage bug: