Yep, heard this somewhere and so far seems to be a decent "trick"....
Set your horse up, and get them to set their head up high (unless you show "uneducated" and make them stretch their neck and head FORWARD not UP if that makes any sense
)
The mane should fall down so that the front part makes a straight line up from the chest. This way you won't see any mane from the opposite side. If you look at the mare in my avatar, you see the dark "dot" above her crest that is her mane ribbon. It drops straight down, right behind the bridle path, and you don't see any of her mane from that side even though it is very long.
Andrea