I'm currently working on this dress (the black with lace at the bottom) which has a long tie belt. (I'm really hoping I do not regret that bulky bow in front.) Having to do some more angled fabric points I thought I'd show anyone interested my method.
First turn up the corner. I guess where it should be and then do a light pressing. Get out the tape measure and measure from the middle of the fold to the outer edge. See my tape measure on the 1"? (I'm using the 1 as my zero mark.) Since I'm aiming for a 5/8" double folded hem, I want my measurement to be 5/8". Which it is, sorry for the overexposure. Photographing black fabric at night ain't easy!
Now check the other side again from the middle of the fold to the edge. It's 5/8" again, so this time I do a firm pressing.
Now cut off the tip, leaving only 1/4" to be turned under. Turn the corner under first, then do the edges. Pins are definitely your friends here.
Here's the corner pinned.
And here's the entire tie. This is one long tie, let me tell you!
Then do a final pressing and ta-da! A perfect point.