there are far and few times you want horizon slanting..to show an uphill or downhill progression..in this case...force the straighten on the horizon..my humble opionon..just a slighty competent amateur..but I got dinged one time by a judge for a fairly perceptible horizon leaning to the right ever so slightly...I had the image blown up 20x30 and custom framed and matted...no one mentioned the tilt..I disagreed with the judge..went home and hit straighten and it moved ever so slightly to the left.