I agree with the other post. For any kingsnake or milksnake in a cage that size, an 11x11 is plenty.
11x17 is more suited to larger-bodied snakes like Boa constrictors.
Neos are fantastic cages. The material holds in heat well enough to get by with low wattage devices.
Hint: If you want to add a little air temp increase (slight amount), get one of those lamp sockets that dangles from the power cord and hang in from the cage ceiling. Example, those 5 1/2 inch dome reflectors sold at hardware stores. You can disassemble the cord from the socket (remove reflector) and feed it through a 7/32 inch hole in the cage ceiling, then reattach. Use a 15-25 Watt bulb. If for a mtn king you do not need this. But for an adultcornsnake or something larger, it helps take the chill off during cold weather without being heavy or overbearing.
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Mark