If its just one point of contact, well, of course there will be A hotspot. (Your flask would be sitting directly on the bulb, yes?) Even if you clean all of the glass very well, it will still be hotter there. Try finding a watchglass that can fit betwixt the bulb and your flask, and set it with the concave side facing up (towards the flask) and fill it with some oil or sand or something)... .. . Use dye. If you could darken your oil with ink or something, more heating would be afforded.
Another guess-possibility would be to wrap the bottom of your flask in aluminum foil. It would distribute the heat effectively. Use a marker and blacken the bottom face for more heating. My little friend Maroon recently performed a reaction using a 20mL long-neck round-bottom flask covered in blackened aluminum foil and a 200watt light bulb. (Swim calls it the "Micro Desktop Ornament")