Child sub menus pushed down too far below parent links

Hi,

I’m using the logo centered, menu below layout, with a widget left and right but when I add a child menu it displays too far down the page and not tucked under the parent link as expected.

View post on imgur.com

I tried changing the height and line-height of

#header_main .container, .main_menu ul:first-child > li a {
height:44px!important;
line-height:44px!important;
}

But this just pushed the main container up through the header.

Thanks.