Hello,
This issue is caused because of the Full Width of the Header and as the Size of the Header decreases on Smaller Devices, the Logo and Menus adjust themselves accordingly to the available width which causes this. You can consider decreasing the Size of the Text in the Menu. Consider using the following CSS Code:
.device-lg #primary-menu ul li > a {
padding-left: 12px;
padding-right: 12px;
font-size: 12px;
letter-spacing: 0px;
}
This should definitely work fine. Hope this Helps!
Let us know if we can help you with anything else or if you find any further issues.