I have mine on the sandbed under T5s and low to moderate flow.
I agree on the lighting and placement with the others.
As far as what you can put them next to: Frogspawn, torch's and other hammers.
WAIT... No torches. They are of the same family, but a torch will kill your hammers and frogspawn in a few hours. Some people have had luck with keeping them close or even together for a few weeks, but in most cases, the torch will kill the hammer or frogspawn.
Trust me.
Not true! Read these, they are all the same family Euphyllia and are ok to keep together, yes even touching.
http://www.reefcentral.com/forums/showthread.php?t=757597
http://www.reefcentral.com/forums/showthread.php?t=2224842
And some great care tips for them
http://www.reefcentral.com/forums/showthread.php?t=2128773
Not true! Read these, they are all the same family Euphyllia and are ok to keep together, yes even touching.
http://www.reefcentral.com/forums/showthread.php?t=757597
http://www.reefcentral.com/forums/showthread.php?t=2224842
And some great care tips for them
http://www.reefcentral.com/forums/showthread.php?t=2128773
+10 on a torch hurting a hammer or a frogspawn.. What i don't know is if a duncan can be next to a hammer/frogspawn.