The rest needs to be in contact with the arrow long enought to "stabilize" it, but at the same time it must have enough time to get out of the way before the fletches contact the rest.
So yes, a longer draw length (longer arrow) will be easier to tune...but a shorter arrow is not impossible.
Also, there are some rests (Spot Hogg, for instance) that drop quickly and will keep contact with the arrow longer...which would be easier to tune for shorter arrows.
Hope that helps.