How to generate decay chains with non-fixed unstable particle masses

Dear experts,

(This may be a dumb question with simple solutions, but I just did not find the correct syntax to make it work. Would be great to hear your suggestions.)
I am trying to generate e+e- -> tt events with exclusive top and W decay chains, in which I want the top and W to have physical width. I tried two ways to write the process, but neither gave me exactly what I wanted.

1. Write a series of decay processes, as mentioned in another question https://answers.launchpad.net/whizard/+question/708455
An example of the syntax I used is
---------------------------
model = SM_CKM
sqrts = 365 GeV

process proc = e1, E1 => t, tbar
process t_dec = t => Wp, b
process tbar_dec = T => Wm, S
process Wp_mn = Wp => E2, n2
process Wm_ud = Wm => U, d

unstable t (t_dec)
unstable T (tbar_dec)
unstable Wp (Wp_mn)
unstable Wm (Wm_ud)
---------------------------
This way I get the processes as I want, but the masses of all the top and W are fixed at their SM value without any spread.

2. Write one process from initial state to final state, and getting intermediate particles with "resonance history".
An example of the syntax I used is
--------------------------
model = SM_CKM
sqrts = 365 GeV

?resonance_history = true
resonance_on_shell_limit = 10
process proc = e1, E1 => (E2, n2, b, U, d, S) {$restrictions = "3+4~W+ && 6+7~W- && !H && ^[W+,W-,A:Z]"}
--------------------------
This way I do get intermediate top and W with mass spread for the majority of the events. But for ~20% of the events, no intermediate particle is found.

Could you let me know if I am using the correct syntax and how I can fix it?

Best,
Xunwu