Pitch Shifting (rotating Heads) need help improving.

Hi,
This patch is actually my first Gen experience. What I want to achieve is a pitch shifter based on the doppler effect.
To avoid clips from the play head I went with windowing. However the phasing sensation which result from the distance between the multiple play heads seems really gross to me (is this coming from my code ?).
If I change the Delay Time too much I get kind of AM sound which I don't want. On the other hand increasing the number of play heads seems like introducing comb filtering.
What solutions do I have to reduce the phasing sensation ? May be a technic to use only one play head and still avoid clip ?
Thanks a lot for your help, and suggestions !
Best regards,
Soall