your installer was "so close" to getting it right...but missed it the shot.

Yes you should use a passive crossover on your tweeter when running active, but it needs to be well below the active xo freq so as to not interfere with the sound of the tweeter when the active XO is working.

Its only there in case the XO craps out and leaves your tweeter unprotected and getting a full range signal that would fry it. There are many articles on what value to use, but look for the one from Andy at Audiofrog, his is considered to be the gold standard. You just need a simple 6db cap inline with he positive tweeter speaker wire...the best value is in the article that andy wrote.