The impact lever does help in the treble. The mid range is no harder than usual to tune.
I carry in the impact lever for these, which usually stays in the car, knowing that I will need it. With the long upper duplex, the very large pressure bars, and the tuning pins without plate bushings, it is far too easy for any "English" on the pin (no offense intended) to end up as unequal non-speaking-length tension. Any attempts at very small corrections just get the non speaking length tension from previous unfortunate attempts to mess up the pitch something fierce. To settle things down, one needs to not only make small adjustments, but to make several small adjustments in a row, till one has washed out the worst of the non-speaking-length unequal tension. In the search for tiny adjustments, a very careful use of impact can help at least a little bit.
The impact lever also helps because it doesn't leave any twist in the tuning pin, and it doesn't cause "flagpoling." Both are very easy to do in these pianos because of the lack of plate bushings.
Yes, coming up to the pitch and stopping helps some. It is far more important than usual to focus on the last direction one exerts pressure, which needs to be upwards.
It's extremely hard to make small changes, yet unless several of the last pitch adjustments in a row are small no stability can be achieved.
In defense of these pianos, they may be harder to tune, but piano students prefer them to practice on because of a rich and varied tone. Also, if one does manage to get them REALLY in tune, the tunings last very well.
I know they have been discussed either in this group or the CAUT group before. Using an ETD is very beneficial in this instance. If my memory serves on previous discussion about them is that You pretty much have to throw your usual technique out the window when tuning them. You pretty much have to come very, very close, or nail the target on the first try. Otherwise you'll be fighting it; it's a fight no matter what…I use a smooth pull technique and find that works best for me. I'm an assistant tech at U. Of GA and there are several in our inventory; not one of them is any easier than the other.
I believe Steinway never attempted to make a great upright piano. And your experience with the studio upright is just another example of the shortcomings of these beasts. A couple of years ago I came across a Steinway studio that I found impossible to tune. When I told my customer that it was impossible for me to get it to stay in tune she said, "Oh the last tuner said the same thing". That last tuner was a nationally recognized technician who has taught many tuning classes at regional and national conferences.