I've tried using 18g poly as a main with nat gut or syn gut crosses. I just don't seem to get any bite on the ball (eg. on a topspin forehand) vs. 16 or 17g poly mains. I'm thinking it is too thin to use as a main. Most recent attempt was at 56lbs with a nat gut cross at 56lbs. Any recommendations or am I stuck with using my two 18g poly reels ina full poly set up?