If you hit a single tree object, it may rip in several pieces, if you hit a forest, it will invariably explode and dissapear. With respect to this hitting-exploding issue, I find realistic settings very unrealistic: any bad take off or landing will make your plane explode as nitroglycerine? Sorry but not, never, nope...
For this aspect, it's much more realistic in easy mode, when your undercarriage or your wing tip can rip.
When you hit the ground directly, It should only explode when your fuel tanks are full, or you're still loaded with bombs and even so, depending on the speed. You can see bombers completely loaded not exploding in tons of documents.
About bombers exploding with AAA hits, I've read some reports for SB-2, but first SB-2 types had unprotected fuel tanks in wings, so they caught fire or even explode quite easy. I don't think this could apply for other planes.
Here a couple of famous pics of a famous Potez-540 fully loaded when shot down (she had departed from Madrid just some minutes before). You can see no explosion there...