Note: the higher the LED peak current, the narrower the output pulse centered about the true zero-crossing. BUT - also, the higher the operating current, the higher the power dissipation in the two resistors. It is a trade-off.
I'm curious why a higher peak current would result in a narrower pulse. Higher current means lower value resistors, which should allow the LED to turn on earlier in the sine wave cycle.
From my post to your thread on another forum:I want to use it for dimming a halogen lamp (220v ac)"