I have DQ6 and installed my new Big Typhoon straight over the top of the Crazy Cool heatspreader, no foam or mylar.

Two points of the backplate extend beyond the heatspreader by approx. 10mm and are therefore in mid air above the MB, about 5mm. I tightened standoffs carefully until a point where bracket starts to bend yet isn't bending the MB. I WILL get some washers or make something of appropriate size to take up this gap (recommended).

There was still sufficient screw length to thread the four nuts onto the heatsink bracket.

No problems - E6400 @ 3.32 54c average during dual-prime (16hrs...)
(although I notice 59c max this morning, where it was only 55c max after hours last night. Ambient temp is now about 3c higher, which explains it.)

Personally I think this arrangement is safe provided you are very careful not to stress the board when tightening the standoffs. The whole heatspreader, sandwiched between, serve to stiffen the board in this area too.

No experience with Ninja though, so check the length of your screws (assuming that that's how you affix it to the MB)