With small ovens these are moot points, if there is a direct line of sight between element and PCB, it is heating your board with IR to a significant degree, that means there is shadowing if you deploy some kind of shield or something tall is on the board. So what you will find with difficult parts is the solder not meting at all, your only weapons are time and temperature but as you fiddle with those; smaller parts can end up getting too hot for too long and. You really want to stick quite religiously to the TAL (time at liquidous) time and max temp ratings of your parts, and that windows is pretty narrow. You really want circulating hot air and as little radiated heat as possible, that gets heat transfer all around difficult areas and prevents weird cold zones, this is why phase reflow is also popular and efficient.
Don't confuse an Oven profile with a board profile, the oven profile is the temp cycle it needs to run to transfer heat at an appropriate rate for the PCB/solder to match its desired profile . An oven will run at far higher temps than the PCB inside it, element or air temp is typically what an oven controller is measuring but for a drawer oven a probe mounted on the board might work better as you are trying to control a single area where the oven and the PCB both lag your setpoints. There are a lot of DIY efforts out there, some may be worth copying, the commercial single zone reflow ovens out there are either crazy expensive or crap. A small single zone oven may also change its performance board to board if used continuously as well as become a bottleneck in your process, there are small conveyor oven out there such as the IN6 (OK performance possibly goes through heating elements) or hybrid Air/Reflow like a T980.
A conveyor based oven will have multiple zones running at preset temps, typically a manufacturer will create a sacrificial board and solder thermocouples in multiple locations with high temp solder, including difficult areas e.g directly under something high mass. They then run this board through the oven and adjust the various zone temps and conveyor speed until all those points meet the criteria set by the solder paste over the reflow process. Our old IR one had zones from ~195 to 330C to achieve what they call a ramp to peak profile. That isn't an ideal profile but it was what that oven could manage with a ~6min process. By contrast our new oven is full forced air convection, with 7 heated zones and I can design profiles where even the last zone is under 260C, this leaves little chance of anything getting overheated as 260C is a pretty typically max temp for a lot of components, it also lets me achieve a ramp-soak-spike profile. Ovens and reflow are more complex than they first appear, at the commercial end of things it can take a lot of money and space to get the performance and throughput one needs.
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