I recently asked this question about usage of a melee attack spell when you are already touching the target. although it's pretty must answered, I had a non-fighting situation in mind and ended up with several fighting situations answers.
So here I reiterate my question for a non-fighting situation : Can we get some kind of leverage from already touching or being in proximity of an eventual target?
Take this situation: You are a caster and you are in a parlay with a foe. Discussion goes pretty well and you keep talking and moving around while arguing as peacefully as possible. You get to a point where both you and your foe are now close to each other. You put your hand on his shoulder (or shake his hand) and your foe confesses an abominable betrayal. At that moment, you decide this parlay was useless and prefer to see your foe suffer rather than become your ally.
Since you are already touching you target, can you get any kind of advantage from the fact that you are already making a contact that would allow you to inflict the spell's effect on the target?