I think I've found it.
I could disable "sleep mode" (at least at P3D 8.2.1) by changing the values "htc_wireless_sleep_start_time" and "htc_wireless_sleep_end_time" in /data/data/com.android.providers.settings/databases/settings.db to "0". Seems to be the time in minutes from midnight.
Looks like these values are introduced in Sense 3.5 and transfered into later installations of (some) Sense 3.0 roms through Google Account, when "save/restore settings to/from Google account" was activated. But I think most of us use this feature, or who likes to install his favorite apps one by one after changing rom ?
As far as I can see on my Google Dashboard the "Android System Settings" of my device are update in my account after changing this entry so I hope they will be synchronised to future installations.
P.S.: regarding not affected Bulletproof 1.4: here the "htc_wireless_sleep*" values are not taken over from Google Account. I don't know why but may be related to different rom bases ???