I don't believe this to be true. When held up to the light, My DC 9mm beaker appears to be 9mm even down in the beaker section. You can look through the glass wall and follow it down the beaker and it clearly stays the same thickness and becomes maybe <1mm less thick in the bend of the beaker. I believe that with some worksmanship, a "true" consistent thickness isn't difficult to obtain. Ive seen it.