As soon as the flash head is moved from the "straight on" position, most of the settings information disappears off the flash display because it is no longer applicable. TTL mode measures the incident light during pre-flash and adjusts the flash output accordingly - until you go beyond the limits of the flash.
So I use TTL mode most of the time (whether bouncing or direct or using a diffuser) and, if necessary, adjust the aperture and/or flash output if review of the shot shows the exposure to be off.
At least, that is my 2 cents worth. Hope it helps. The FL-36 manual is not particularly informative on this issue.