Greetings
I use the distance setting of the elertas as a function of the speed, so warning is given around 10 seconds.
Assi, do not warn much in advance; nor too close, not to resettle to brake sharply.
And I configure for each type of alert, because in some of them I use fixed distance.
Example below:

warn_distances=150:420,140:390,130:370,120:340,110:310,100:280,90:250,80:230,70:200,60:170,50:140,40:120,30:90,20:60,10:30