I haven't got a tremendous amount of experience with the glue except for applique and bindings, but this is how I do it. For smaller pieces, I use your a method using a tip on my glue. For bindings, I also use a tip. For pieces that I really want to be perfect, with no chance of any glue getting where I don't want it, I turn the pieced article upside down, apply the glue to seam allowances and then put the batting on top of that and iron. Then I go back to your method A on the backing and apply the batting/pieced part to the backing. My best advice is to use a tip just about all the time that you use the glue. You don't need much glue to get it to work very well. So far, I have not thinned my glue, but I am going to try that on my next charity quilt.