Carbing a RIS

So I have a Russian imperial stout I plan to bottle soon and I want to know how much corn sugar to add. I plan on pitching 4g Nottingham right before I bottle so there is viable yeast.

My problem is I only have 4.5 gallons possibly less for which I would usually use 3/4 cup corn sugar but I am afraid that would make it too fizzy. (I believe a RIS shouldn't be highly carbonated correct?)

If you like the carbonation level with 3/4 c in 5 gal, just scale it down by 10%. If you want lower carbonation, 1/2 to 5/8 would be a reasonable range.

If you're going to go by volume, I would just go 1/2 cup or a wee bit under for an RIS, and if you've been aging it cold I'd go even less.....a little fresh yeast sounds like a good idea to me too.

I personally use beersmith to determine the proper amount by weight of corn sugar for the specific level of carbonation I want (eg. 2.1 vols for the oatmeal stout I bottled yesterday came to 2.87oz of corn sugar) I just weigh it out on my hop scale. You can get much more accurate levels of carbonation this way. you're kind of winging it with the 3/4 cup for every batch, and overcarbing for many styles that way.

Ok about 1/2 cup seems to be what you are suggesting but if weight is more accurate how many grams/ounces would you suggest?