do you use a tower on your kegerator?
if so, your situation would lead me to infer that the reason you get a good head is the beer in the line is warmer, making it foamier. when you wait, the beer in the tower gets warmed up, leading to another headier pour.
you could shorten your lines a little, leading to more head on consecutive pours, but could lead to overly foamy first pours.
Kegged: Berlinerweisse, Dubbel, Galaxy Wheat
Bottled: Golden Strong, Mild, IIPA, Rauch
Fermenting: Saison, Imperial Wheat Stout, Brett Saison, APA, Brett Roggenbier