It's possible to be at zero heel lift but it will take a lot of work and boot fit trips. The primary thing you want to look for in boot for max heel hold is the shape of the shell. Most rec shells are just tube shapes, simple cylinders that get their shape from the liner. Get into the burlier race boots, especially plugs and semi plug boots (95 last width or smaller) and you'll see more of a teardrop shape in the cuff. This is the shape you really want for maximum heel hold.
Here's where all the boot work comes in. Plugs and semi plugs are not meant to be worn straight away. The shells are extra thick so that you can carve out a custom shell. It's a long process (took me around 12 visits to get mine dialed right), but well worth it if you really want your foot completely locked down. My heel would rip off before it lifts in my current boots.
This is a intensive process and not for everyone. You can certainly ride just fine with a bit of lift. If you are like me and picky about having that rock solid fit with absolutely zero lift, it is possible to get there.
Otherwise, more common and less costly solutions include adding foam butterflys or j bars, you can buy these off tognar.com they just adhere to the outside of your liner. Or you can look into high density liners like intuition, make sure you get their extra dense liners not the normal alpine ones they try to sell you in most shops. Also zipfits have a good rep because you can add more material as they pack out.
As to how much is too much, it's all up to you and what you want.
