First, VTA is adjusted by ear not eye. Nevermind how it looks. Raise it up a bit and if it sounds better it was too low. If it sounded better and better as you were lowering it, and when you are as low as you can go you are sure even lower will be better, then yes shim it. The best way by far to do this will be to buy some fO.q tape. This will both improve the sound a lot as well as effectively lower VTA. Then if one piece isn't enough and you want even lower, put another piece towards the rear of the cart to angle the rear lower. Use the rest of the sheets all over your arm, table, and other components. A very effective tweak sure to bring out lots of low level detail.