Yeah, these non-pro ovens have a pretty nasty rep. There may be a "sweet spot" in the oven somewhere. I do pretty good by doing small batches in a toaster oven that I retrofitted with a heat-ramp-soak controller from Omega, and putting a thermocouple directly on the board. especially after insulating the walls of the oven.
If there's a way to move the temp sensor to be in direct contact with the board, do it.
Other than that, all of these non-pro solutions, my retrofit included, take some hours of cycling through while measuring, to tweak out the ramp-soak profiles. Ya gets what ya payz for.
Also, if I may, you don't use an oven like this for real quantity. Therefor, if you don't need to use lead-free, don't!! You have less of a chance of burning up your board at a lower temperature. In addition, you might think of this as a prototyping step. Use your oven to inexpensively knock out prototypes, test them, then ship off board assembly to folks with the right gear.