And what do you lead back from Q852?
And what do you play from Q852 when partner get on lead and continues the suit with an honor? And with a small one?
And what if you have Q102 what do you play when partner on lead continues with ...
Playing UDCA you always show your origin length.
1. Play the 7.
2. 3 and 7 - showing origin even number.
Playing standard you play the same cards but now showing present length.
These rules make you play technically correct card when you return partners lead having Hxx from start.
IMO best way to play diamonds when you suspect W led from short clubs is to take DK and run D10. Then you can get 4 diamond tricks when E has 9x or 8x.
And if declarer finesse early for W to have Q9xx or Q8xx he will be in ...