From a tweaking standpoint you are on the right track.
Pull the back up and neckline down, pull the shirt out of the pits and sleeves further down on the arm. Also, rotating the seam on the sleeve towards the bicep will help, as well.
Your best bet, however is to alter the shirt. Two things. Sew in a wedge at the seam where it ends at the cuff. You will basically be taking out a a little less than half an inch in sleeve diameter if you do start the stitch right where it is thickest when folded over. This will help the sleeve stay in place (not slide up as the bar descends) and provide more pop from the chest plate.
Additionally, just like every Centurion needs to be taken in at the middle of the harness, both a Fury and F^ need to have the "moons" taken out. What I mean by this is place a stitch on both sides of the chest panel that decrease the 'roundness' of the current stitch (when the shirt is inside out.)
Be forewarned that this will change the feel of the shirt and you will need ample time in it before a contest to adapt to the changes.
The easiest alteration is the cuff one I described. Probably start there first as most people are surprised how much that tightens up the chest panel.
Then, assuming you have a seamstress up to the job, take the moons out of the chest panel.
You can PM me and I can send a pic of both alterations.
Lastly, use powerwash. Everybody with a poly shirt should be using it.
The trick is to put the shirt in on the last rinse cycle of your washer so it just gets agitated with the powerwash and spun. You don't want to rinse it out. Powerwash will stiffen up the material.
Don't apply unnecessary heat to the shirt. That's a dumb idea that's just going to fuck it up.