Most ski boots come with straps, which can be of several types. Let's take a quick look at the straps and their use:
simple straps, which are not elastic and can be put under the plastic "fat" straps, which cover both plastic and the top of the tongue, sometimes with independent adjustments "booster straps", which can be put over or under the plastic. Normally, the strap should be placed under the plastic, on top of the tongue, for a more progressive flex and quick response from the boot.
Higher-level racers tend to put the boosters over the plastic and very tight, for a quick response and feel.