The Friday 7.30pm episodes do quite well relatively speaking with shares of about 40%. They've been getting about 8.5m recently, and considering the Thursday episodes get 7.5m, you'd have to say that Tuesday episodes up against Holby City would be down to about 6.5m-7m which would be unacceptable really for what is still ITV's best-rated weeknight show.
On Thursdays, Corrie would be half an hour long most weeks so that would give the BBC an opportunity at 8.30pm to try pre-watershed comedy and other things. Friday 7.30pm would be a prime spot for sitcoms to rate well, between The One Show and EastEnders.
Essentially I don't think moving 2 episodes of Corrie around and 1 episode of Emmerdale to simply boost Tuesdays is worth the hassle, when it will have a negative impact on Corrie and will open up more slots for the BBC to make inroaRAB in. It's also not something which fans of Corrie will like as it breaks routines/habits which are years old and some viewers might not watch the Tuesday episodes and in addition to the Thursday episodes which don't rate anyway, they might say it's not worth keeping up with the show anymore, and it'll have a knock-on effect on how the other episodes rate.
The programmes which air on Tuesdays are cheap factual shows anyway so it's not really essential for ITV to get big ratings for them by giving them a Corrie lead-in. Don't get the false impression that if Corrie were to move to Tuesdays, they'd suddenly start commissioning dramas for Tuesday 9pm or expensive live shows. They'd probably still have the same old factual stuff!
Also we must remember that even with Corrie lead-ins on Thursdays, some shows at 9pm have been rating with just 3-3.5m viewers or so (Greatest Cities in the World, All at Sea, Homes From Hell). What's to say the same thing won't happen on Tuesdays?
You're right that BBC1 hasn't really taken advantage of the lack of Corrie in that Wednesday 7.30pm slot; I think other than LoR, Jimmy's Food Factory got 5m+ but cant remember any other show. On Sundays at 7pm, however, they've made real strides since Corrie moved away from there with the success of Countryfile. And I think on Friday 7:30pm they'd have more of a chance of succeeding because whatever show they have would be airing right before EE and I just think they'd make more of an effort there.
Yep, it must be desperate times at ITV HQ for them to re-run a whole series of Grimefighters in the Autumn

.