I think it depends on whether you are ordering in anticipation of another course coming or if you are getting extra food beyond what you planned on ordering.

Say that you have had this happen a couple of times, and now you go in for lunch. You could look over the menu and say we should split an app and we will each get an entree. If the chef pops out a 2nd app along with your regular order, then I would tip the usual plus a couple of extra bucks.

If on the other hand you say, let's just order a couple of entrees, because they will probably send out an free app, then I would tip heavier.