When ordering from a menu many (particularly - but not always - first time) customers are focussed on the choice and making decisions about side dishes, and only when the order is served do they see the amount they have ordered - with comments such as 'I cannot eat all those chips / meat' or look a bit disappointed about how much is on the plate, or indeed the fact they cannot fit in the pudding!
Portion size varies between restaurants, but ideally the customer needs to be served the correct amount to give them a good experience and to avoid waste.
Would it be an idea for an appetite choice to be included on menus - smaller / normal portion - to prompt a discussion with the waiter up front?
You also have the problem of the brand drumming it into the food server to up sell like crazy.
With the wine not so bad but + chips + garlic bread + peppercorn sauce..... so on and so forth.
(I bet you can tell where I eat) Thus turning an economical bill of £40 for 2 up to £50-55. Changing what could be a weekly event in to a less frequent special occasion event.
www.primanox.org
I think customers' expectations vary depending on the restaurant they go to.
If your portion are not standard: like tapas restaurant, maybe steak house or maybe oyster bar you could possibly write a few words on the menu to give a bit of guidence. This is as well a great occasion for waiting staff to interact with the customer.