Could you post a picture of your block? The only way I can think of to lose the points (after the block is attached to sashings/ other blocks) is if the seam allowance joining the HSTs to the rail fence squares is too narrow. The method you use for the HSTs won't matter, as long as they are the same size as the other parts of the block and are pressed so that the seam is perfectly diagonal.
Is it just that the points look like they're missing because you're looking at a completed block that isn't yet attached to anything? If you lay a ruler so that you can see where the final 1/4" seam will finish the block, do the points end up where they're supposed to be? The points do look cut off in a completed block that still has its outer seam allowance showing.