Feedrate changes not affecting Z plunge rate

Hi All;

I'm trying to write a surfacing program that slows the plunge rate of the spindle. I've tried:

G0 Z-0.005 F3

and 
F3
G0 Z-0.005

Neither change the feed rate of the plunge. However, when using G38.2 combined with an F3 in a probing routine, the spindle slows as expected.

Does spindle plunge rate not respond to the Fn modal command or is there something that I'm missing?

G0 is rapid, and not uses F value.
Use G1 F3.