Proximity to heat source is positively correlated with cooking time. Mine is 4" off the manifold, and corn dogs take 3-4 hours to get real hot, even in the summer. But they're less likely to burn, so there's always a trade-off.
Also keep in mind where your drips are going to go- preferably on a heat shield, not the manifold itself. There's a potential for cracking that you want to minimize. And I chose to mount mine level, so I can bake w/ sauces, etc. and have fewer drips. Finally, make sure you can get your stuff out fairly easily, with gloves on. No tricky hose clamps or anything, no laying on the ground... you want easy access. HTH...
82 fj40, 99 uzj100, 06 gx470
97 DR650, 05 525EXC, 01 XT225, 89 TW200, 09 TTR125, 07 TTR90, 07 CRF50