Without the shim or some type of shim I can’t get the arm parallel to the record surface unless I use an extra thick mat which I’m afraid will change the sound maybe for the worse.
then you need a mat like SAEC SS-300 or anything same thickness instead of something between the cartridge and headshell.
Do you have a problem with every LP with real music or just with Hi-Hi Test LP ?
Not every cartridge can pass the suspension test on Hi-Fi Test LP, especially the last two grooves with very high modulation, only a perfect cartridge can do that, most of the cartridges will jump out of the groove.