A bit off topic, but I stopped sandwiching concentrate between flower when that method is needed. I find the herb gets too roasted and affects the flavor of the concentrate. If you have it, try wrapping your concentrate in a tiny piece of organic cotton or hemp fiber. You only need a small flattened piece of cotton, the size of a dime. The oil spreads throughout the fibers of the cotton which prevents leaking into the heater and it also increases the surface area of the concentrate. I still wouldn't use a huge glob of concentrate, but I have never had oil leak into the heater or out of the bowl of any vape I've done this with. The oil stays within the cotton fibers. Also, there's no mess with gunky sticky used flower. You just toss the used cotton and start again. Keeps your heating chamber pretty clean.