Replying to Rail Spotting

So recently I've tried the smaller of my mountain's C boxes, and an up box. (I'm not sure if thats what its called but just a box that goes straight up with a little panel to stall on the top)

Right now I'm at the point just getting comfortable with having enough speed to actually be able to do the whole thing, but I was wondering where you spot when you are on these?  Do you still spot the end of the box like with straight ones or do you sort of look a little in front of you and spot up the box until you are near the end?

Any general tips for these types of boxes, on weight distribution or whatever, are also much appreciated.