I don't know what the fx billiards "acid test" is, a preliminary search gave no conclusive results. I presume it's some sort of draw shot drill?
You should choose drills that work on the areas at which you are weak. So the fact that you are struggling is a good sign. It means this part of your game needs work. HOWEVER, if you are not making progress, you are probably doing something fundamentally wrong, and to make matters worse you are setting those bad habits in concrete, by repeating them over and over. Videotape yourself, and watch carefully or upload it and let others watch it. If that doesn't show anything too conclusive, try setting up a draw shot into a small pocket and gradually increase the distance, shot by shot. The moment you feel yourself starting to struggle, try to notice what is happening in your stroke.
If it's a drill which requires lots of draw, and you are missing and/or not getting as far back as you want, I can make some educated guesses, without even seeing you play. I'm guessing that you are jerking your cue back, which either throws your entire stroking line off or messes up your back-to-forward transition in your stroke. This can both cause you to miss your object ball target and your cueball target (tip position). If that is not the case, you are likely either throwing your shoulder in to the stroke to get power, or dropping your elbow too much or prematurely. There could be other things, but I'd check for those things first if I were you. Hope this helps you.