depth of the vibrato

Programming and Development Nyquist
1

Hello Sirs.
I wrote a code in LISP.

(defun mytone ()
 (mult 
  (pluck C2) (pwl 0.5 0.9  1 0.9  1)))

(stretch-abs 4
 (scale 0.75 
  (mult 15
   (mytone) (lfo 6))))

I would want that the envelope PWL acts on the amplitude of the vibrato (depth). The code is thus bad because the envelope acts on the intensity of sound generated by the Nyquist Prompt. To observe it, it is enough to replace pluck C2 by sine 48.
My question is thus the following one: it is possible to act on the depth of the vibrato, without acting on the volume of the string?
Beforehand, I thank moderators who will take time to answer.

2

You apply a tremolo to the sound and that’s a “trembling” based on modulating the amplitude.
Vibrato is always a Frequency modulation (like lengthen and shorten a string by shifting the fingers left and right).
But You’ve already experimented a lot with ‘fmosc’.