Arrow rest always mounted horizontally?

[Rangeball]

When adding a new rest to a bow, should the rest always be mounted horizontally and then adjust the launchers up or down as needed to produce the desired arrow location? I'm wondering, as I replaced the welded metal launcher on my savage drop away with the teflon v-spoon launcher, and it seems that when I shoot with a feather down, contact is occuring. I know I can easily solve this by shooting feather up, but am just curious if how to best mount a rest is a hard and fast rule.

[Big John]

No it is not a hard and fast rule. An example is the old 3d rover rests, the prongs are short so the rest should be tipped down in the rear for better clearance of the "down" vane. Looking at the riser from the string side, the horizontal bar of the rest should be even with the horizontal riser cut-out.