We played at a local HS that had a about 250 LF but quickly out to 300' after maybe 30'. They played it is a dinger. So no, I've never seen a down grade of a ball hit out, but I've seen the opposite.
A local field a dinger is awarded if a ball hits above a line in the LF wall, yet still stays in the yard. It's an 8'fence, 310 all the way around except a huge section 30+', protecting a parking lot.
Also one that has light poles inside the fence from L to C, with big tall pads that extend well above the 6' fence. Hits above the pad it's a dinger.
Swing over to R the score board and light controls are boxed inside a kickout (kick in, in this case), ball inside the kick out 2b, off the scoreboard and in, dinger.
Yet, another with a tree hanging well above and weil into LF field, hits the tree and stays in 2 base, hits the tree and goes out dinger.