Why not use two 1.5 Uf or three 1.0 uF in parallel? Crossover values should match exactly.Too small and you will have a mirange hole. Too large, and you have a mid hump, and may overpower the tweeter.
That is consistent with the tweaking I did on my polk sl2000 tweeters.
A 2.2 uf/250v didn't block enough of the mid-range frequencies from getting to the tweeter so the tweeter was still a little harsh. A 1.0 uf/250v did the trick in most cases by changing the crossover point a bit lower than the 2.2 uf as indicated in my signature.
Caps block the lower frequencies from getting passed on down the signal path.