There are a lot of ways to brew high gravity. Most make compromises on efficiency.
For styles like barleywines, only the first runnings are traditionally used. First runnings are usually about 20 P. and you'll just boil down for gravity.
Then, traditionally, the grain would be sparged for a second, "small" beer."
If you're trying to limit the water to increase the gravity, this is why you're sticking your mash. You simply have too much weight on the screen. An alternative might be a reiterative mash. This is where you run a normal mash (and sometimes sparge), then pump that wort back on top of a new mash. The second mash with the wort picks up a lot of sugar. You then sparge it out and will have about 22 to 28 P wort in the kettle that you can further concentrate.
This works best if you are making an intentionally high gravity brew. If you are trying to make high gravity wort in order to increase capacity, it's probably best to stay at 20 P or below because of increased esters and tired yeast that may not always attenuate.