Large space between LI when only two boxes shown - why?

body {
  background-color: #D6ECEF;
  font-family: Helvetica, sans-serif;
}

header.commerce1 {
  background-color: #D2691E;
  color: #FFFF;
  border-radius: 5px;
  padding: 22px;
}

a {
  text-decoration: none;
}

div.content {
  background-color: #FFF;
  width: 860px;
}

body {
  font-family: sans-serif;
}

ul.stock {
  display: flex;
  flex: 1 0 20%;
  flex-grow: 3;
  flex-wrap: wrap;
  flex-basis: 100%;
  width: 800px;
  margin-left: 16px;
  margin-top: -40px;
  list-style: none;
  margin: 1px;
  justify-content: space-between;
}

ul.stock li {
  font-family: sans-serif;
  font-size: 88%;
  color: #333;
  background-color: #FFF;
  column-gap: 3px;
  border: 3px solid;
  margin-left: 40px;
  margin-bottom: 10px;
  max-height: auto;
  width: 250px;
  margin-right: 0px;
  margin: 0 0 20px 0;
  justify-content: flex-end;
}

ul.stock li h3 {
  font-size: 1.2em;
}


/* 

ul.dealers li h3 {
color: red;
}
*/

ul.stock li p {
  font-size: 0.75rem;
  width: 230px;
  white-space: initial;
  padding: 3px;
  margin-right: 20px;
}

ul.stock li img {
  height: 180px;
}

a {
  text-decoration: none;
}

hr {
  height: 1px;
  background-color: #a2a9b1;
  border: 0;
  margin: 0.2em 0
}

p {
  margin: 0.4em 0 0.5em 0
}

p img {
  margin: 0
}

ul {
  margin: 0.3em 0 0 1.6em;
  padding: 0
}

ol {
  margin: 0.3em 0 0 3.2em;
  padding: 0;
  list-style-image: none
}

li {
  margin-bottom: 0.1em
}

dt {
  font-weight: bold;
  margin-bottom: 0.1em
}

dl {
  margin-top: 0.2em;
  margin-bottom: 0.5em
}

dd {
  margin-left: 1.6em;
  margin-bottom: 0.1em
}

h3,
h4,
h5,
h6 {
  margin: 30px 0 0
}

h2,
h3,
h4,
h5,
h6 {
  padding: 0;
  position: relative
}


/* 
h2 {
font-size:18pt;
line-height:24pt;
margin-bottom:0.25em
}
h3 {
font-size:14pt;
line-height:20pt
}
h4,
h5,
h6 {
font-size:12pt;
line-height:16pt
}
*/

h2 {
  line-height: 24pt;
  margin-bottom: 0.25em;
}

h3 {
  line-height: 20pt;
}

h4,
h5,
h6 {
  line-height: 16pt;
}

ol,
ul {
  margin: 10px 0 0 1.6em;
  padding: 0
}

ol li,
ul li {
  padding: 2px 0;
  font-size: 12pt
}

q {
  quotes: '"' '"' "'" "'"
}

blockquote {
  overflow: hidden;
  margin: 1em 0;
  padding: 0 40px
}

h3 {
  margin-top: 10px;
}

hr.archive-aex {
  border: 5px dotted #ff0000;
  border-style: none none dotted;
  color: #fff;
  background-color: #fff;
}

#content {}

[id="Content"] {
  font-size: 14px;
}

.mw-body {
  padding: 1.25em 1.5em 1.5em 1.5em;
}

.mw-body {
  margin-top: -1px;
  border: 1px solid #a7d7f9;
  border-right-width: 0;
}

[id="bodyContent"] p,
.vector-body p {
  margin: 0.5em 0;
}

[id="bodyContent"],
.vector-body {
  font-size: calc(1em * 0.875);
  line-height: 1.6;
}

div.stockimg img {
  width: 250px;
}

<header class="commerce1">
  <h2>MY AUCTION SITE TEMPLATE</h2>
</header>
<div class="content">
  <h3>T-SHIRTS SALE</h3>
  <ul class="stock">
    <li>
      <div class="stockimg">
        <img src="https://upload.wikimedia.org/wikipedia/commons/e/e6/LIOR_FOR_ATHENA.JPG">
        <p><b>Women's T-shirt</b>, white <b>WAS £10.00 NOW £5.00</b>
    </li>
    <li>
      <div class="stockimg">
        <img src="https://upload.wikimedia.org/wikipedia/commons/thumb/5/5d/11_p_edit_edit.jpg/800px-11_p_edit_edit.jpg">
      </div>
      <p><b>Men's blue T-shirt</b>, Size M <b>WAS £8.00 NOW £5.00</b>
    </li>
  </ul>
  </div>