Lu.
It's coming. Consider;
With an offset flapping hinge, there is no 'remaining 18-degrees'. This is because the swashplate and the tip path plane became coplanar in 72-degrees.
With delta-3, the rotor must revolve a number of times before the swashplate and the tip path plane become coplanar. Here those 18-degrees do have an effect and the magic words just might be 'washed-out coupling effect' and 'Wee-wa'.
heedm
The phase angle is the number of radial degrees between two events. In the case of a rotor it is the input (pitch) and the output (flap).
You are correct. " the phase angle is reduced precisely by the amount of delta 3"
On a rotor with flapping hinge offset, the blades fly to position faster. Therefor the phase angle (phase lag) is less than 90-degrees. On a delta-3 rotor, the phase angle is also less, but for a very different, and more complex reason.