Empty p elements will rarely create a space on any ADE based eReader.
Code:
<p class="calibre4 sgc-4"></p>
Try:
Code:
<p class="calibre4 sgc-4"><br /></p>
or:
Code:
<p class="calibre4 sgc-4"> </p>
instead.
Or better yet, create another css class that applies a "margin-top: xx" value, that can be assigned to paragraphs that need space between them and the preceding paragraph(s).