Well, that's a nice problemYour high efficiency is due to have. :) You haveusing a couplelot more water than you need, washing every last bit of options:
1/ Collect less liquorsugar out of the mash. Ultimately, acceptyou want to collect less wort. This will result in a lower efficiency. 90% efficiency is neatAs such, but no one says youyou'll need to maximize your efficiency; you're not in a competition. Collectuse more grain to account for the pre-boil volume you needlower efficiency.
2/ Use less grainIf you had 22L at 17°Bx, then you started with 35L at 10°Bx with 90% efficiency. With this optionIf you instead want ~25L (assuming about a 10% evaporation for a 60 minute boil, you're going to target the sameymmv) at ~15°Bx, and assuming 75% efficiency, but you're goingyou might need to use less~30% more grain and thus less water.
X units grain * 90% extraction = 10°BX * 35L , and should end up at a happy medium where you're getting high-efficiency from lessX = 388
Y units grain and still hitting your target gravity and pre-boil volume* 75% extraction = 15°Bx * 25L, Y = 500
500/388 = ~1.29
Some mix of those twoBut your brewhouse is probably the right solutiongoing to have its own particulars, so brew, measure, math and repeat.