To be perfectly honest, I find it doubtful that your tails are washing out due to being too far forward on your boots. If so, then you are probably doing half a dozen other things wrong that need to be addressed first.
I feel you are possibly getting some misdirected advice here. Projecting your hips diagonally during turn init in order to keep your hips more forward is desirable pretty much always. If your outside leg is extended, then in order to project your hip forward, your ankle will need to be flexed and you WILL be pressuring the tongue of your boot. SOME joint has to be used to move your hip forward. Your leg is straight and if it were bent it would only move your hips back, not forward. Flexing the ankle is the only way to move it forward at that point. Stand up right now and keep your knees only very slightly flexed. Now move your hip forward without changing the flex in your knee. How do you do it? You can only do it by flexing your ankles which means pressuring the tongue of the boot.
That is not the reason your tails are washing out.
If the tails are washing out, there is something else going on. Please send us video. Speculation has been made here and I feel it may be counterproductive for you.
If your boot is setup properly for fore-aft, then as you extend your leg into the new turn, you should feel the arch of your foot, possibly the back of the arch. NOT your heels. If you need heel lifts or boot work, you might feel the balls of your feet, but that should still not cause your tails to wash out, it would just make it more difficult to remain stacked is all since standing on the balls of your feet is more strenuous than standing on the entire base of your foot. Your fore-aft balance is determined by the location of your hips relative to your feet. You can definitely be aft-balanced and feel the balls of your feet and vice versa with heels. Your boot setup can effect things too. Needless to say, I find it extremely unlikely that the only reason your tails are washing out is because you are too far forward. Most skiers have to work hard to get more forward.
Wash out occurs because you didn't engage the edges or destroyed your edge in some way, quite likely from pushing or extending too hard or abruptly or skiing with too much energy and not enough finesse, using too much rotary movement, etc.
Please provide video and we can give you better MA.