Having rebooted to stock and tested volume wake on that, there's not much difference to minimoto.
Two taps of up/down vol wakes stock.
Two taps of up vol wakes minimoto, but not down.
Am just checking the keymap files as I've not consciously modified these, but a small difference may have crept in back in V1.2 on when I first used /etc from mavrom to get it booting under safestrap.
[edit] nope, keymap is bit-for-bit identical to stock, but never mind, have found a way to implement vol key wake properly here :-
http://xdaforums.com/showthread.php?t=1585309
The technique needed some modifying to work with D3's keymap and our own implementation of isWakeKeyWhenKeyguardShowing(), but it works like a charm for both vol up+down with only a single tap. Note that the volume wake won't work for 2 seconds after the screen is locked, while the phone descends into full sleep mode.
Weird.. I have had single tap wake on all roms I've ever tried except this one.
Will try the method you mentioned