IS-4M being more bomb-proof than Object 279 describes explicitly the issues with overpressure and explosion logic overall. Bombs ignores cover, meaning, you can be behind a wall, if the vehicle is weak enough you can recieve enough damage to be destroyed and so on. This is a rather small detail however could add so much to the game, an actual fragmentation simulation that interacts with the surrounding serving as protection or not.
the reverse-no-armor bug is still there but now its on HEAT ATGMs
the turret roofs are known to be quite thin T-44 and onwards, only really protected by the ERA, however if something big enough goes off, the ERA itself would not be enough to protect it