exact same thing happened to me, but i bent the tube so i had to get a new one and the new one never fit into the hole at all. I believe it's supposed to go all the way in until it hits the stop on the tube. i havn't had a dipstick in a year, it sucks.
I'm in the middle of a shortie install myself. On my dipstick tube (92 5.0 engine) there are two collars. One is 2 3/8" from the bottom of the tube; the other is 3 1/4" from the bottom of the tube. The tube should insert into the block all the way up to the first collar - so 2 3/8" of the tube should go into the block. I've been pleasantly surprised that with the Ford Racing headers, the dipstick tube goes right back into the exact location it was in with the stock headers - no bending or adjusting at all.
I sent the tube through the header, instead of around it.
The bracket does not connect to anything, but I can hold it down with my hand when I want to remove it, via the bracket that connects to the header bolt.
I really should connect it to something down the road.
For now it works fine... Gotta compromise sometimes!