I noticed, many, many times when I dropped a Satchel charge on the back of a Sherman it would stay even if they drove away. However, the Satchel only damages it until like 70%. I would imagine it would kill any tank instantly, isn't this a bit odd?
Also, I'd solve this by throwing two satchels, by the preparation process of the Satchel just takes too damn long. I've tried putting two on the back in a row, but before I could throw the second one, the first one already went off, killing me in the explosion. I'd have to wait for the first one to go off, but obviously, the tanker would be alerted.
And usually they run off, and since the tank is still 100% functional at 30% health, Satcheling a tank is almost useless. Perhaps there are more vulnerable places to put the satchel? Personally I think one Satchel should just kill medium armour in one hit.