Spreadheets embeds are iframe. You can simply change their size by applying the CSS property "height" to them.
For that, go to Appearence > Customise and add the following code.
iframe {
height: 10rem;
}
To avoid changing the size of all the iframes on the site, even those that are not spreadheets embeds, you need to add to the CSS rule a selector that allows you to change only the size of the desired iframes.
For example, one could identify a specific CSS class on a page containing the embed and add it to the CSS rule.
For example, we could have,
.page-id-1237 iframe {
height: 10rem;
}
Thus, only the iframe on the page with the class .page-id-1237 will have its size changed.