Shrinking header animation speed

it correlates with scroll speed – so no animation / transition speed here.
Slower scrolling is the solution

or if you like this – maybe it is a satisfiing solution for you:

#top #header,
#top .av-logo-container ,
#top #header .av-main-nav > li > a,
.logo a, 
.logo a img {
  transition: all 3s ease !important;
}