Speaking of war goals, I am on the camp of Russia will grab big instead of small like "just west of river" and "just connect to crimea".
First lets define the minimums. Kherson, Zaporizha are already in process of integerating into russia. These two russia will not let go. Luhansk and Donetsk are no brainers basic initial war goal. What about the rests?
Hypothetically speaking Russia could be perfectly happy with these gains, and secure a neutralized Ukraine as client state. But will it really go that easy? No way Ukraine will just surrender even if it seems rational to cut the loss at that point. Therefore the war goes on.
As Ukrainian military disintegerate, westerrn stocks run low, the economy collapses, Russia will advance further, and have less of a reason to give back. They will advance faster and faster. Cities will fall one after another and Ukraine will stay on the fight. Russia will obtain Odessa, dnipro, kharkov, and even Kiev. And Ukrainian government will still be too stubborn.
At this point Russia can just call it a defacto win and attempt to roll over and police rest of ukraine. Or Ukrainian people finally had enough and coup the leadership. Either extreme scenario is more likely than a flat surrender.
This means either Russia grab all of Ukraine and spend time police it, or at least hold enough land to cause collapse of Ukrainian society. No matter what there can be no "call it a small win and go home".
The so called maximalist gain of grabbing most of ukraine west is really a very conservative estimate. It is far more likely to go above it.