That’s what I was using before, but my problem is my bed is fairly significantly warped… Inflexible glass fixes this entirely and I’ve had absolutely no issues with adhesion. At least not with PLA or TPU.
Although thinking about it I could clip the PEI to the glass giving it a flat bed…
I dunno, I use a mirror tile heated to 60⁰C. TPU and PLA seem to stick just fine. Have you tuned your first layer height?
I also give it a good scrub with isopropyl between prints.