PrimaCreator FlexPlate-Powder Coated PEI 510 x 510 mm

I've got a Creality CR10-S5 (510mm x 510mm Print bed), and I'm trying to print a large briefcase lid, having had no success at first, the lid kept detaching itself from the glass print bed, after a few months it was suggested that the heater plate was too small at 310mm x 310mm, I removed this and replaced it with a 510mm x 510mm Silicon Heater (240Vac x 1300W), this allowed me to print the lid onto the GLASS printer bed using 3DLAC without it becoming detached from the print bed, but the finish of the surface was too glossy, so it was suggested that I try the Prima Creator FlexPlate Podwer Coated with PEI ULTem (Polyetherimide), the Flexible plate comes in two pieces, the sticky magnetic portion is stuck to the print bed, then the upper portion is placed onto of that, the question I'm asking is do I stick the magnetic portion to the metal bed, or the glass bed? Anyone have any ideas, many thanks.

The steel powder coated plate is your printing surface. As it is steel, it is attracted to magnets or magnets are attracted to it. If you attached the magnetic portion to the steel plate with the adhesive, there would be nothing to hold the plate to the glass. By attaching the adhesive magnetic sheet to the printer, the steel plate is then available for printing and also easy removal and flexing to pop free your prints. Exercise care in attaching the adhesive to your printer, to ensure there are no bubbles or variations in the surface, as it will create an uneven surface on which to print.

Thanks for your speedy reply, that makes good sense, the way the glass print bed was held to the aluminium bed was by 8 small bulldog clips, so I'll stick the steel plate to the Aluminium Bed plate, of course making sure that plate is clean, then the Gold Prima print bed will magnetically attach itself and can be aligned perfectly. No more Bulldog Clips, which used to get in the way anyway.