Just thought I'd jump in since we have LO the same age and I am having a rough go, too! (See "18 month old sleep is all over the place").
I am experimenting with set nap and BT as well. This is the 4th day and so far, I am doing ok. DD schedule is this:
7:15 wake
12:30-1:40ish nap
7pm bedtime (she falls asleep by 7:30).
She has always been on the lower end of sleep needs and also never been a good napper, so I'm not too worried about OT. However, last night she had 3 NW (9:15, 10pm, and 2:30am) and I'm wondering if they are OT related after a few days of 13 hours of sleep. I have committed to doing this for a week so I will reevaluate then.
Good luck!