The mare and I both had similar expressions on our faces . . . like, "No, we ain't goin' NEAR that stuff . . . we are totally in agreement."
My mare and I have a contract - I don't put her at anything big and ugly, and she jumps whatever I put her at. She has only refused me once, and I have ridden her from the start (she is an ex-broodmare who wasn't broken until she was 14). She was right to refuse too, because I was very uncertain about the jump. We were out on a cross country course for the first time, and the jump was what's called a "coffin" - a telephone pole on the takeoff side, and a ditch, about three feet wide and four feet deep, with planked sides. It looks very nasty from the saddle - like it's yawning for your reception. I didn't like it either, so she just dropped her haunches and stopped one stride out. We got a lead over for the second attempt and we were both fine. She hasn't refused anything since.
Three feet is not all that big, if you work up to it gradually in the ring. I think most of the jumps in our hunt country are three feet and smaller . . . typically the stone walls are maybe two feet, the coops anywhere from 2 1/2 feet up to three. I don't like to jump the mare any bigger than 3 feet in any case, she's 19 now and I want to keep her legs and feet in good condition.
That coffin jump sounds like the name is accurate!
I think 3 feet is a good sized jump. It looks really big when you are cantering up to it! (I'm such a chicken) I'll bounce over some 18"ers to 24"er's but bigger than that, they really start to feel like jumps and I lose my nerve. I honestly don't know what happened to me to make me so nervous about jumping. As a kid the biggest jump I ever took was 7 tires (with a plank across), bareback. Just the thought of doing that now puts me in a cold sweat.
I go to the Grand Prix jumping competitions when they are in town and those jumps are humongous. A fixed jump that size, like the olympic ones you described, are just nuts. Incomprehensible.