Glad to know I'm not the only one just getting their corn started. I don't know what your temps are but I guess if it's started germinating it must be above 65f, so that shouldn't be the problem. I've found it a little sporadic myself, and if you had problem with your seed it could be that. I went with an open pollinated variety (Early 'Double Standard' Bicolour) as it's a proper open pollinated seed it is widely adapted, and adaptable to future change in climate or soil, and it hasn't been bred to need lots of fertiliser and sprays. So, can do well in different soils, climates and variable weather. I've never grown 'ambrosia treated sweet corn', so don't have any idea to it's specifics, but if your having issues with it my suggestion would be to try a true open pollinated variety. Plus, if you selected and saved your seeds it would improve to your local area over the years, not to mention you wouldn't have to buy seed again.
Also, just an idea, but if you have problems with drought a technique I saw used in a very dry part of Argentina was to have a trench around the crop, as you would for irrigation. In theory I guess that this would get more water, deeper, around your corn, might not be much use if you've got clay though.
That's my two cents, excuse my ignorance if I'm missing something with the ambrosia treated corn.