It's all about the depth of the centre channel. Do a search through the forum and you'll find quite a bit on setting up Trifield.

Basically, to summarise these learned threads and my own experience, the centre channel snaps into place and 'disappears'when you get the depth right. The fact you can notice the centre channel suggests you haven't got it just yet. It's quite noticeable when you get ti right, it's not fluffy like the 565's phase settings.

Main system: 818v3, 861v6, HD621, Oppo 103D, DSP8000PP, DSP7200SE HC, DSP3200, SGR Sub
Family room: HD621, 861v6, DSP5200 L/C/R
Headphones: Schiit Mjolnir v1, Sennheiser HD800; (office) iFi iDSDPro, Focal Elegia