edit ./Themes/default/GenericControls.template.php
change by inserting "style="height: 300px;" so it now appears as:
<textarea style="height: 300px;" class="editor" name="', $editor_id, '" id="', $editor_id, '" rows="', $editor_context['rows'], '" cols="600" onselect="storeCaret(this);" onclick="storeCaret(this);" onkeyup="storeCaret(this);" onchange="storeCaret(this);" tabindex="', $context['tabindex']++, '" style="height: ', $editor_context['height'], '; ', isset($context['post_error']['no_message']) || isset($context['post_error']['long_message']) ? 'border: 1px solid red;' : '', '">', $editor_context['value'], '</textarea
I also inserted // Personal Preferences: Modified from the default 175px size of Editor window
just prior to the above.
Thanks SirOsis from SM.
Now implemented.