On a spherical Earth there MUST be a slope, otherwise you agree the Earth is flat.
You cannot use thermal inversion when we have clear photographs taken from some 240 m in altitude. Thermal inversion (looming) can be used as an argument in the case of eyewitness accounts who are located on the beach/shoreline of the point of observation; in the case of clear photographs, thermal inversion cannot make a 59 meter curvature simply disappear.
We can see the shoreline of Toronto NOT in spite of a 59 meter curvature, but in the absence of such a visual obstacle.
I'm not sure you get it. At 240m there is no slope
in the way. There is still a slope for sure, but a line of sight calculation that can be found here
http://en.wikipedia.org/wiki/Line-of-sight_propagation says I can see over 55km from a height of 240m without the Earth's surface getting in the way. If you're arguing you don't notice any downward slope, I'd argue of course you don't as It's too slight to notice.
As far as the one taken from the lower altitude I don't know. Like I said I'd like to see that picture taken again around the same area in winter and compare the results. That'd remove the question of a looming effect. As far as looming only occurring when you're on the shore line I'd say is false. It's a matter of where the thermal inversion is taking place, and to what extent it's taking place.