As between the two SQ routes with First Class across the Atlantic to SIN, it's actually Houston that has the bigger discount (measured as a reduction from the "normal" or unrestricted first class fare). An IAH-SIN round trip in first is almost exactly the same price as JFK-SIN vv in first....but it's a good deal longer trip.
Even the discounted F fares are pricey. The SQ "RTW" FEZSQ fare is a much better deal.....and it's available from any SQ US gateway.