With a single knife wielding attacker, it was from 3 or 4 feet out to 20 feet. Exploding off the X isn't contrary to what I'm talking about.
What was taught in the class was you want a stable platform during the moments you're shooting. You don't want your feet dancing or running while you're shooting. You aren't taking up a full isosceles or weaver stance. You aren't pausing to sing the full course of "row row row your boat" before taking the next step.
You move perpendicular to the attacker, away from their weapon, drawing while moving. Even at 3 feet, the perpendicular move provided enough separation to allow drawing from strong side concealment. You pause your feet and turn your body towards the attacker just momentarily so you have a stable platform and then fire from retention. You move again perpendicular to the attacker, away from their weapon. You pause momentarily again so you have a stable platform and fire from retention.
My experience in the class was that people that didn't do the pause to get a stable platform (move and shoot) missed a lot and got stabbed (with a fake knife obviously). The people that paused when shooting (move, then shoot) hit the attacker almost every time before they could be stabbed (the class assumed multiple shots to the attacker before being stabbing stopped the threat).
That was my experience. YMMV.
Forget it. If you follow it you might die.
I respect your effort to learn, yet I think you were ill advised. I have fought adversaries with guns and knives at close quarters, and I am able to write this post because my training kept me alive. It is past my bedtime so forgive typos. I am tired.
Stepping aside in a knife assault will get you stabbed! When you step aside you lose continuity of defense, a critical component of fighting. Then you have to regain it, that is to need to readjust into fighting mode. inam speaking about defensive composure. If you are unarmed, it is much better to stand your ground and concentrate on the attacker's knife hand position. If you have learned how, it is relatively easy to take the knife away. Not as easy as taking a handgun away, but easy enough. The secret is to stop the arm and disable the wrist. Since I could write a book on that topic, I'll just stop there.
If you are being attacked by a knife neither the Isosceles nor Weaver position are of any value, but Weaver is better because it offers cover of vital organs better than Isosceles.
Today there is a better option.
By luck I had the good fortune to meet Paul Castle around 2002. Paul, who died in 2011, was the creator of the the Center Axis Relock (C.A.R.) gunfighting system. He was a proven warrior in the British military and police. He designed the system from decades of experience. If you want to learn more about the C.A.R. System start here:
http://www.sabretactical.com/CAR.pdf
The C.A.R. Gunfighting system really makes the Weaver and Isosceles stances obsolete for close quarter combat. If you really want to educate yourself in self defense, you must evaluate the system. While I value the many things I learned in the Corps, the C.A.R. system is better when it comes to civilian self defense.
I have no financial or otherwise economic interest in any entity offering training in the System. I write about it only because it is a life saver. Learn about the System and then re-evaluate your thoughts on this thread.