For 2 1/2 half sqs use two 6 in squares. Use 8 in for 3 1/2. Just add 2 in for each size. You do have to square up after cutting. Draw an x thru sqares with right sides togather. Sew 1/4 in on both sides of lines.
Cut at the half way of sq both ways then cut on drawn lines. You will have 8 half sqares.Example for 6 in sq cut at 3in on both sides of sq.
For flying geese you take the size you want the lenght to be and add 1 1/2 in for the first square then add another 1 1/2 in for the second square.
The larger sq is the points.
You should be able to watch El Burns video for flying geese on her web site.
It is really simple but hard to explain without pictures.