Actually, they are not slanted at all. Just an optical illusion.
In #1, the edge of the base is not parallel to the shore if you look closely. So it looked slanted if you judge the 'slantness' from that part of the base. But if you check the tiers of the pagoda, they are basically horizontal. Just scroll the picture up and down the screen and use the edge of the window to check.
In #4, it is opposite. The base of the pagoda in this case is horizontal but due to the height of the pagoda, the resulting perspective shift made the edge of each floor look more and more slanted as the nos of floors increased above ground level.
The best conditions to take IR photos are bright sunny day with clear blue sky and some clouds regardless of whether the cameras are modified or not. Those taken during the group outing to Chinese Gardens looked just as dull to me and not sharp to boot due to the overcast conditions and the slow shutter speeds required I suppose.
The modified Sony actually also give the best results during bright sunny days with images that jump out at the viewer like these:
I do agree though that the E-300 does give very nice IR photos under bright sunny conditions. Still need to use a tripod though unless it is overseas like in my Italy shots.