Everyone has different taste thresholds. If you felt 4 oz on a 19 lb grain bill was too present, the roasted malt probably won't mask it enough to make it a subtle flavor addition.
Start even lower. Go with 2 oz.
I always start low with specialty grains and will increase the amount the next time I brew a recipe if I feel I didn't get all the flavor out of the grain I wanted. It's better to make something drinkable but less unique than something undrinkable but unique.