Again - my experience in torpedding Russian ship is only from 1.0 version - don't know how it would be in 1.5
But in 1.0 I didn't find any difficulties to hit immovable ship - even from margin distance. Sometimes more save/load tactics help
Especially when your dumb miners don't throw torpedoes as expected - look at this like at the bug
Can your please tell - what is going wrong when you play? You can't get close enough to release torpedoes? Or they miss? Or what? Hitting a moving defending ship with torpedo is sometimes a complex task - but stalled ship should be easy targets, shouldn't they?
I usually target every DD individually - as they are not smart enough to attack in division. The point is to track target in fire range for a some time - to allow miners to prepare torpedoes. And the other problem - despite that they miss too often - you may push an enemy ship with 4 or 5 torpedoes none of which is exploding or leaves too less damage. In this situation save/load often helps