If your arm does not allow for VTA on the fly, it will always be different depending on the thickness of the record. That's just part of analog. If things sound a little dull, you can try raising the back of the arm slightly or change the tracking force a bit. The tracking force sometimes makes a big difference. Some people cannot live with the variables present in the analog world - always obsessing about adjustments until it becomes a source of stress instead of enjoyment. Just goes with the territory.
