Do you send in your extensions Blank? Or calculate each one?

I'm filing extensions for everyone that didn't make my cutoff date, and it occurred to me I might be doing it the hard way. I wanted to know how you guys create your extensions. Ultra tax lets me just select all the clients needed and send in blank extensions for all of them at once, but I never do it that way. I go in there and calculate an estimated balance due for each one based off of last year and things that changed recently, and it's too much work.

Do you coordinate with your clients to make sure their extension payments match what you put on the form?
Do you just send in the extensions with the amount blank and let the clients submit whatever payment they like and not worry about it?
Do you not trust your clients and submit payment for them?

I'm curious how others operate in this regard as I think it might be better to just discuss with the clients who have no idea what they'll owe rather than discussing with each and every who owed last year that I file a balance due extension for.
*This was re-done as my last post was not formatted up to standard