I think you're fine only because of the equipment you're using.
The snake blocking the heat from being delivered to the probe may cause the air to rise and the tstat to turn off.... But will it do it in time to not give the snake a burn from above? Will that even work at all? That's my worry. If the snake puts it's cold belly on the probe what happens then? Will it still detect the air warming? I agree the snake's size may help under the current circumstances but at some point things will need to be changed.
As to snakes moving. If snakes always moved when the heat was getting too hot we shouldn't see burned snakes from run away heat mats, lamps, or flexwatt. They should have felt the heat and moved but we know that's not always how it goes and burns happen.
I mainly bring this up so others seeing your cage and this thread don't blindly copy it and cause harm to their snake. It seems that in your situation if we changed even one thing we could have issues.