Ok, I am going 
to try and explain this as best I can. When you are building a "flat" ride thereis 
a small yellow arrow that lets you know which way the ride is facing as well as 
where the center is. This isn't the center of the ride but is the center of the peeps focal point. 
Any scenery that is place within a 5 square radius of that arrow counts twards that ride, it doesn't matter 
what scenery you use, You can mix and match if you would like. If you built the sphinx and a tree they 
would both help that rides excitment the same If you place a "flat" ride next to the parks borber, and 
scenery that is within that rides 5 block radius will count! However indoor rides such as: the haunted 
house and the circus show arent effect by theming at all. There are a few other things you could do to effect the 
ride, such as changing the legth of the ride, however if you do this you are going to either make the queing line 
longer or shorter, by this I mean make it shorter so that alot of guests can't get in line so in turn they can't 
get mad about waiting there forever.
So in conclusion: Theming near "flat" rides is almost essential if you wan't your park to flourish, 
but you can effect the excitement of these rides by different options if the rides screen, 
but remember indoor rides will not be effected by outdoor theming.