That would assume that the Max has been a runaway success, and was produced in larger numbers than the XS. The evidence seems to show that Apple did not quickly sell down its initial inventory of the Max, though (so they have over-predicted initial demand compared to previous releases, and the total sales volume will probably slip compared with previous Plus models). Apple must surely be hoping that significantly more than 50% of unit sales go to the XR so that it can continue to sustain growth (higher profit than the 8/7, but less than the XS). Expect a massive advertising campaign!
2.5x may well be conservative if Apple can trigger the demand.
The question is whether Apple has deliberately priced up the XS, knowing that it won't sell, in order to boost XS Max sales and allow a quiet increase in XR prices, or has simply been caught out by consumer resistance to the price point that it intended for its main product.