Hi GTM,
The smallest P-TTL flash I've found is the Metz 24 AF1. It's
P-TTL only, uses 2 AA batteries, has a low trigger voltage (anything that works with P-TTL will use a low trigger voltage), the reflector tilts a full 90 for bouncing, and a GN of 24m, and usually sells for $89.99
Metz mecablitz 24AF-1 Digital Flash for Pentax Camera MZ 24317PS
Metz also makes an Auto Thyristor/Manual flash that's identical in size and weight, also with a tilting reflector -- the 20 C-2. It's even cheaper at $50. In manual mode, it only fires at full power.
Metz mecablitz 20 C-2 Auto Flash MZ 20220 B&H Photo Video
If you want the smallest possible flash that will work on a Q, then you might try the Sunpak PF 20 XD. GN 20m (ISO 100), does not tilt, 3 Auto Thyristor modes, Manual from 1 -1/32, slide up diffuser screen, uses 2 AAAs and can be used as an optically triggered slave and set to fire on either the first or second flash.
Sunpak PF20XD Auto/Manual Digital Slave Flash PF20XD B&H Photo
I have all of these, and all work fine within their parameters, but I have not tested them extensively for exposure accuracy under a lot of different conditions and settings.
For the two Auto thyristor/Manual flashes, you need to turn flash "off" in the flash menu or they won't fire.
Here's what the Metz guns look like on a Q:
The Sunpak is about the same dimensions without the portion that extends forward, essentially a rectangular box, it sits horizontally on the Q, and has a much smaller reflector.
BTW, these flashes work well on Pentax DSLRs if you have one -- super compact and light convenient to carry in the bag all the time. The Sunpak, as an optically fired slave, can be used to give more creative lighting with the pop up or another external flash.
Scott