Opto Triac driver (moc3051) basic circuit problem
Your issue may be with the particular load and trigger current pulse you are using for the higher voltage. 

The current has to have sufficient time to build up to the holding current for the triac or it will not stay on for the remainder of the cycle (it will just momentarily conduct for the duration of the trigger pulse, much like a transistor). The triac is deliberately made a bit insensitive to keep from false triggering (eg. dv/dt).  

Inductance in the load, too much series resistance in the gate circuit (1K is a bit on the high side) or a too-short trigger pulse can all contribute to this. 

If a DC trigger level turns the main triac on reliably then your problem is related to the trigger pulse.