无法从div获取一致的y轴值

Question

我正在建立一个新的投资组合网站，但在从div返回一致的y轴值时遇到问题。

我尝试使用scrollTop，目前使用getBoundingClientRect从div中获取axis和top + bottom值来更改滚动背景颜色。

我的HTML：

<main class="main flex">
<header id="mainContent" class="main__content flex">
            <h1 id="contentTitle" class="content__title">I design things that communicate.</h1>
</header>
<article id="coverPg" class="main__cover flex work__article--active">
            <img alt="div1" data-category="Print, Typography, Layout" data-bg="7e288b" class="cover__item" src="media/TT5.jpg" />
            <img alt="div2" data-category="Print, Illustration, Typography" data-bg="CFD4CE" class="cover__item" src="media/hl6.jpg" />
            <img alt="div3" data-category="Poster, Web, UI/UX" data-bg="7CB8C0" class="cover__item" src="media/t2.jpg" />
            <img alt="div4" data-category="Web, UI/UX, Mobile" data-bg="7CB8C0" class="cover__item" src="media/t2.jpg" />
</article>
</main>`

我的CSS：

body {
    background-color: var(--yellow);
    height: 100%;
    overflow-x: hidden;
    overflow-y: hidden;
    position: relative;
    -webkit-transition: all .5s ease-in-out;
    -moz-transition: all .5s ease-in-out;
    -o-transition: all .5s ease-in-out;
    -ms-transition: all .5s ease-in-out;
    transition: all .5s ease-in-out; }
.main {
    position: relative;
    height: 100%;
    z-index: 1;
    overflow-y: auto;
    padding-right: 17px;
    box-sizing: content-box; }
.main__content {
    position: fixed;
    right: 0;
    left: 0;
    margin-top: -2.5vh;
    height: 110px;
    z-index: 100; }
.work__article--active {
    position: relative;
    height: 100%;
    padding-top: 85%;
    display: inline-block; }
.cover__item {
    max-height: 50vh;
    width: 100%;
    object-fit: cover;
    margin-top: 7.5%;
    margin-bottom: 7.5%;
    box-sizing:border-box; }

有问题的JS函数：

trackCover = function(workDOM) {
    var contentPos = document.getElementById(DOM.content).getBoundingClientRect();
    var percentage = Math.round(bodyDOM.getBoundingClientRect().height / 7.5);
    for (var i = 0; i < workDOM.length; i++) {
        (function(i) {
            var workPos = workDOM[i].getBoundingClientRect();
            var active = new IntersectionObserver(function(entries) {
                if(entries[0].isIntersecting === true && workPos.top < (contentPos.y + percentage) && workPos.bottom > (contentPos.y - percentage)) {
                    console.log(`${workDOM[i].alt} is ${workPos.y}`)
                }
            }, { threshold: [0] });
            active.observe(workDOM[i]);
        })(i)
    }
};

应该发生的事情是，一旦元素在main__content的值范围内滚动（这里是contentPos +/-百分比），它将从滚动到div的数据值中拉出。

它最初是有效的，但在向后滚动（沿任何方向）时，我会遇到一个y轴值变化的墙（5到20之间的任何位置），滚轮移位从〜-200到〜 500。