You might be underexposing those print films, and the lab could be compensating. Try a test with slide film, which is much less forgiving, to determine the real guide number.

That said, I suspect those units should be able to handle bounce flash in a small room. I do all this stuff manually, so I'm not sure what to tell you about your TTL system, but I suspect that if it's just underexposing, there is a way to fool the system (say by adjusting exposure compensation or the ISO dial either on the camera or on the flash) to get it to put out more power.