Help with tone arm geometry and bass

After installing a new cartridge, I checked that my SME 309 tonearm was level. The sound of voices especially male voices was a bit bass heavy. so I added a ringmat turntable mat which raised the level at the head shell by 2mm. The bass heaviness disappeared. This is the opposite of what I was led to expect. I always thought head shell up meant tail down and more bass. have I got it wrong?

I would like to dispense with the ring mat so I can use a record clamp on the spindle. But this would mean tone arm level again. Which way do I adjust the tone arm to remove the bass heavyness without the mat?