Good shiz in here. I was always luck in that it was always lower category racing or masters and even when I am in form I weigh more and have a lower center of gravity than most other riders. I put the bars up and then come over. Slowly. Backing into the space is a great technique that almost always works.
I've also been shut out and guttered for miles and miles making me want to punch everyone but at the same time admiring their ability.
I love it when someone asks and always yield to that.
If they only point though and I don't know them - they're getting a hood up their ass.
I've touched, pushed slightly (directly on the hip).
In general you learn what works for you for your size and for the areas and fields you race in. Getting to know everyone helps a ton especially if you're not an a-hole. Many times I hear after the race, "Then some guy shoots the corner and I'm like setting up to sharpen my elbows and I look and see it's f'n Dave so I let him in and yell at him."
Big benefit - if you are close enough then start riding and racing at a velodrome. You learn real quick how to become narrow and fit into tight places as momentum can sometimes carry you into a place where a space doesn't currently exist.