In your child theme’s style.css file find
.sf-menu li:hover ul,
.sf-menu li.sfHover ul {
left: 0;
top: 45px; /* match top ul list item height */
z-index: 99;
}
and change it to
.sf-menu li:hover ul,
.sf-menu li.sfHover ul {
left: 0;
top: 28px; /* match top ul list item height */
z-index: 99;
}
Tested in Chrome only on Win7 so your mileage in other browsers/OSes may vary.
worked like a charm. many thanks.