I actually have a problem with being expected to clean my plate, my mum and stepdad thought there was something wrong with me if I didn't and I still remember throwing up after overeating to please them. DH had a hard time convincing me that he didn't just want me to eat for the sake of it and it was ok to have food left on your plate.
Cleaning my plate, or anyone in my family cleaning their plate, was never a concept foisted upon me. I think because my grandma grew up with it when she was in the orphanage, you cleaned your plate, you let nothing go to waste, so she never did it with her kids and in turn my mom never did it with me. Sure she tried to encourage me to only take a little and reminded me I could always go back for more later, but if I didn't clean my plate, oh well no big deal I wasn't as hungry as I thought. I never understood my friends who would moan about their parents playing the "Kids in Africa are starving so eat your chicken" card. Didn't make a lick of sense to me, plus why keep eating after you're full? Just have leftovers later. Yeah, we'll keep asking you if you want more food, and we'll fix you a snack as soon as you walk in, but if you are actually full (remember say stuffed), then you're full. That's what they made to-go containers for.
Actually a lot of food stuff in my family might have deeper roots then just a cultural thing. My grandma grew up in a orphanage for much of her childhood (she was a ward of the state), and there wasn't ever enough food and sometimes you might go hungry and too bad if you did. So as an adult, there's always a lot of food and no one will ever go hungry. Food was always about love for her. It makes her happy to fix meals for people and see them happy and eating.
Oh, one more word of advice. Do not hesitate. Either take the food or don't take the food. Hesitation means you aren't sure if you should take more even though you want more, you'll be pressured to eat more. It's frustrating. I've learned the hard way. And learn to say "Seriously, it's great, but I'm stuffed, really, truly stuffed, I'm gonna need bigger pants, it was so fantastic!", a little drama goes a long way in family. Now if you do want seconds, remember Ray Romano's stand up, it's "Yes, I'll take seconds" if you want a whole second meal. And "No, I'm good" (not stuffed), if you want just a little more.