Just a little something to explore. I have fought to get from an average kicker to something better for a long time. Having had 2 discectomies, permanent nerve damage and all manner of the proverbial ‘bad back’ list of issues I had slowly become so overly tight in my hip flexors/posterior chain that it was quite simply impossible to demonstrate the necessary hip extension. Over the past 6 weeks I have had 3 extremely not fun deep tissue sessions to unlock these areas. Can’t recall the name of the PT test to determine hip extension, but I have picked ~ 30 degrees of hip extension from first test to last. So essentially I had none when I started.
In short, inflexible ankles and all, my kick is so freed up and it shows in my kick sets and especially my full stroke times. If you have had some injuries, back issues I highly recommend at least finding out if your hip extension is in an acceptable range. YMMV, but if it works you won’t regret it!