I've started making my own sugar-based hobby rocket engines and I want to work on creating a de Laval nozzle for the specific fuel type and configuration I'm using. I don't have the resources to measure things like chamber pressure and exhaust temperature, so I wanted to try and develop an experiment to figure out at what point the exhaust velocity hits Mach 1 and where the nozzle should begin to diverge. If I understand the principle, at the optimal throat diameter is the largest diameter where the exhaust reaches Mach 1 and past that, the flow is choked and only the mass flow rate will increase. My idea was to build a series of engines with converging only nozzles and increasingly smaller throat diameters and to measure the thrust of each design. My hypothesis is that as the nozzles get smaller, I should see the thrust increase until the optimal throat diameter is reached, after which the thrust will plateau, or at least the delta-thrust will be significantly smaller. Is my thinking on this correct?