Primary/Secondary Size relationship

[Irrelative-at-aol-dot-com (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

When creating the primary of a tesla coil, does the secondary have to fit 
inside the primary or can it "hover" above it.  For example, if you have a 4" 
PVC, but the inside diameter of your primary is 3", can you still use them so 
long as the secondary is high enough away to prevent sparks from jumping?  
Ok, so maybe this question is seeming less hypothetical as you read it, but I 
just want to see if I need to get a larger primary or not.  Thanks to all the 
experts who keep us informed!