No, I don't have a different ICR when I'm not using Symlin. I intentionally paired the grapes with peanut butter to help ease the spike. Which fits in with your next question about bigger, fatty meals. I don't change the ICR or my dose of Symlin when I have a higher-fat meal. I wear an OmniPod though, so I am able to change how the bolus is delivered and I do extend my insulin dose with a higher-fat meal.
One would think Symlin would help with a snack, like grapes, just like it does with a full meal, but there must be some residual benefit that carries you close to the next meal. I know I didn't spike yesterday :)
I wasn't much help with this, but as I said, excellent questions! I know I will be paying much more attention to see if I notice anything that I might not have made the connection to before.