I agree with others that out to 35 yards, your 1-ounce load of #6 lead out of an IC choke should work just fine. I also shoot a 20-gauge 2 3/4-inch 1-ounce load of #6 lead when hunting with good dogs, but usually have a 3" 1 1/8-ounce load of #5 lead for the second shot.
It would be nice if you would confirm you load/choke combo's performance at 35 yards, so you will know what that combo does before shooting birds.
Here are a few of my pattern numbers with those 20-gauge loads to give you an idea of what you might get.
Patterns from a 20-gauge Browning Citori with 28" Invector-plus barrels and Briley flush chokes (patterns average of five, 30" post-shot scribed circle, yardage taped muzzle to target, and in-shell pellet count average of five).
20 GA 2 3/4" RELOAD (BLUE DOT)
1 oz #6 lead (233 pellets) @ 1200 fps
30 YARDS – SK / pattern 147 (63%)
30 YARDS – IC / pattern 168 (72%)
40 YARDS – M / pattern 146 (63%)
40 YARDS – IM / pattern 163 (70%)
20 GA 3" RELOAD (BLUE DOT)
1 1/8 oz #5 lead (190 pellets) @ 1220 fps
30 YARDS – SK / pattern 140 (74%)
30 YARDS – IC / pattern 149 (78%)
40 YARDS – M / pattern 138 (73%)
40 YARDS – IM / pattern 147 (77%)
Good luck!