Keep it simple! Reduce inventory and choices that are time consuming (for customers)...that is, at least, for syrups.
As for the 20oz, if you've already got that established at your shop it might be a hard sell for your customer. Let me know what you come up with!
gary, about 2 years ago i decided to bring the 20oz on board, and i'm glad i did 'cause it helps with my bottom line. i figure, if a customer doesn't want 20 ounces, then he/she most likely won't order it, and choose either the 16 or 12. with my particular locations, i get a good amount of repeat customers, but sometimes certain customers will be tied up with events and can't get back to order perhaps as often as they'd like...so they "stock" up on the 20oz! i started out offering more syrups than i do now...quickly found out that most customers weren't ordering the oddballs all that often...so, i stick with about 6 of the basics. get strict!
the coffee hound
It's been about five months since I changed up the menu; so far it's been great and I've really enjoyed it. It's made ordering decisions less complicated, easier and quicker. Every once and a while I'll have someone ask if the 16oz is the largest that I carry, but they always seem content with it and come back. I've never had anyone leave because I didn't offer a 20oz. I did have a couple people leave because I didn't carry their favorite syrup, but to be honest, that doesn't bother me that much. They don't really love coffee, they love the syrup. While I would love to introduce them to what coffee should be, I don't mind if they leave. Another plus is that it provides a gateway conversation to quality coffee. I am in Billings, Montana and am the only genuinly quality-oriented shop here, so people want to know why I do things differently and why my coffee doesn't 'taste burnt' ... limiting my sizes and flavors gives me another way share knowledge and taste experiences.