I incubate at 82-83 and almost never get a male. 79 is pushing it in the low temp department. I'd go with 80-81. The incubator is only as good as its thermostat and the ability of the egg box to keep a very steady temperature. If you're talking about incubating the eggs in the enclosure, or in an empty enclosure with the enclosure's heating pad, people have had eggs hatch that were buried in the lay box but I don't know that the hatch rate is so high. If you mean making an incubator and using a UTH as a heat source, once again, you need a good thermostat that can keep an even temperature. If the room that the incubator is in will get hotter than the incubation temp (which happens at my house because I don't have AC) then the eggs will also get hotter unless you have an incubator that can cool.
Now, this is just circumstantial evidence (and I'll know more after this season), but until this past season I used a mini-fridge type incubator that seemed to have problems regulating the heat if the ambient temperature changed drastically. Consequently, there could be several degrees of fluctuation in incubation temps. I got about 10% or a bit more deformities including notched eyelids, missing digits, leg bones or loose hip joints. This past season I used a new incubator that keeps the temp to within half a degree and I had no deformities. I also had a smaller number of hatchlings, so we'll see what happens this season.