As someone who has taken the blown beads workshop with Davide Penso and is using only the inner fire of a Scorpion (which is a cricket) to do them, I would like to suggest that the heat of the torch is not the problem. As Davide taught us, you literally have around 15 seconds to blow the bead from a hot gather to completion. Perhaps you are taking too long and the glass is cooling? What climate are you in? I have made blown beads bigger than a 3cm diameter on my Cricket with a 5lpm concentrator (which I know does not have great purity). Before rushing to buy a hotter, bigger torch, perhaps honestly analyse your technique and see if that could be the problem. Good luck!