Gas burners and 4-stroke glow have a higher exhaust temperature than 2-stroke glow, as a result they generally smoke better. Very few people are happy with the smoke production from 2-stroke glow engines. It can be done, but it takes a bit more messing around (a pre-heater would help, maybe even a battery powered pre-heater. I haven't seen this approach in person, but I've read about it being done. Simple enough concept, but a fair bit of work)

Also, it's pretty obvious that the larger the engine, the more volume of exhaust, which means you can dump more smoke fluid in there and get more smoke.

For the smaller planes, a pyrotechnic approach might be in order. There's at least one company selling smoke devices that are small and light enough to even work on many park fliers.