All of us who use i-TTL or CLS have cursed the dreaded eye-half-closed look the preflash produces.
There is, however, a way to avoid that by separating the preflash from the shutter by assigning FEL (or FV lock in some manuals and menu systems) to either the Func or the Preview button. The setting is found under the Controls heading in the custom menu.
With the button assigned, you can now activate the preflash and hold the button while your subject's eyes open again, and then shoot. This raises the keeper rate to the region of manual flash, but with the convenience of TTL metering.