Hello again F1nut and all,
I think that perhaps I was unclear in my last post. Yes, I am talking about a shunt cap. And as for 3 in your post, I was thinking of say a Mid Driver working from 6-800 hz to tweeter cutoff. The cap might be a 30- 60 mf (values chosen as an example), and if I put a film cap around it, I thought the film cap would pass the higher frequencies with less smear, and the NPE the lower where the energy stored has more time to be released.
And now that I have read this, maybe the film cap should only be 20-30 % of the total value, keeping the lower frequencies in the NPE.