The vacuum former came supplied with a wire mesh in the bottom of the bed. This lifts the item you're forming off the bed stopping it from blocking the vacuum hole. I decide to make myself a new vacuum bed that fills the area snugly and has a more uniform arrangement of holes. Thankfully the laser cutter is very good at making sheets of holes. I cut it out of 5mm acrylic, a sheet full of holes was held aloft on smaller dots that allow plenty of air flow under it. My thinking was that although the acrylic will eventually warm up I'm only heating the plastic for a minute or two and the plastic sheet provides a perfectly smooth surface. I was wrong, after I vacuum formed half a dozen items at once the sheet ended up pretty flexible and started to warp so I ended up remaking the whole thing in 6mm mdf instead. That's currently working very well but if it shows signs of degradation I'll just send off to have one laser cut in metal instead.