The EOM usually will not be perfect. I tried to speculate the voltage for the EOM at hand. The calibration measurement of the EOM was done by manufacturer at 1310 nm. 

Vpi = 508V @1310 nm

Vpi = a * lambda + c (can fit the voltage by sine)

Given formula by manufaturer; Vpi = 0.361 * Lambda - 23.844. 

Vpi at lambda = 1310 shoud be , Vpi = 449V

But, since its different, I try to calculate what Vpi should be at 1064nm.

for Vpi=508,c==23.844, a should 0.406. Therfore at L = 1064, Vpi=408V

for Vpi=508,a=0.361, c should 35.09. Therfore at L = 1064, Vpi=419V.

The constant are determined by the crystal size, and they can't be revealed by the manufacturer. 

So, we need not just 365V, but around 419-408V, for maxmimum modulation depth.