I always pull it over.
I'm weird I trim/pull the mane and always leave the forelock to get really long.
H's forelock was just under 12inches when I measured it and the rest of her mane was hogged/roached.
I think it depends on the horses hair as well as the preference of the rider. If I put it under I like it braided or if the horse doesnt have a lot of forelock hair. I think it looks to bulky if the horse has a thick forelock and it is shoved under the browband. I would rather it be over the browband to show it off if it is long and pretty. I ride western so most of the time I use one ears or have nothing on the ear or across the face so I don't worry with it much.