I have two TI Buddies. One I practice with 5-6 days a week, the other can only join us for 3 days (usually). It really makes a difference. Improves the focus. Also great to discuss what light bulb may have finally gone on and which ones are still not wired correctly. We tend to mirror each other.
The 1000 Whole focus was mainly breathing (try 5 stroke bilateral as much as possible and patient hand awareness) and trying to hold form. Interestingly, we discussed how much more aware we are now of our 'faults'. Every thing goes along pretty smoothly for a while and than something changes. So the focus changes to getting back to the groove. Today I had moments where my entry was leaning towards centerline a little, focus back on wide track. Had a short stretch where lower back was a little strained, focus on relaxing neck/shoulders. It is nice to be able to recognize some things on the fly and get it back.
I dont know if that answered your post or not. Probably could have a more defined focus on the 1000 or 750 or 1650 or ??, but it seems like the focus subject rears its head while swimming and changes as the swim progresses.