I almost always do it since I don't eat large meals. I rarely order an entre, sometimes I do order two appetizers as my meal. I usually tip by looking at the price of something that I would have eaten had I ordered an entre. For example: I rarely eat beef, not for any dietary or allergy reason, just not a huge fan. I tend to eat a lot of chicken and lamb and pork. The portion sizes are just usually too large for me so I only eat half of what's on my plate if I order an entre and leave the rest, which is a waste and I don't usually carry a bag so there is no way to carry (or heat up later for that matter) left overs around the park. So I look at what the price would be for a dish I would have eaten had the portions not been to large and tip according to that (sometimes the two appetizers are actually more expensive, in that case I tip based on those).