If you're savvy enough to be moving Amex MR points to SQ, you definitely don't want to be using the "pay with KF miles" option. It is primarily designed for people whose entire 7,000 mile balance is expiring in 10 days' time who want at least a SGD~15 discount, even if it's little better than a kick in the teeth.

It is not designed for people who are otherwise looking at redeeming F or J Saver awards. The value for F or J tickets tend to be most closely linked to Full awards.