If you're pressing 660c keys down far enough to actuate (and they're heavy relative to most 45g) then you must be partially pressing down your blues as well since the startup for blues is far less than what it would take to collapse the domes on your Topre....
Reading a
topre switch wiki entry, I noticed the following in the "Key Feel":
You can not feel the mid-stroke actuation point.
I think with my blues, when resting my fingers, I may be lightly 'rocking'' (for lack of a better word) my fingers on the keys just above the tactile actuation point. This might come from my FPS WASD muscle memory, where I'd lightly alternate the pressure on A/D ready to alter direction quickly.
With a topre switch, if I lightly press on them, since there's no tactile actuation, you don't notice when you're actually activating the key.
I'm now testing on the fc660c vs 87u 55... when I try to activate a key as lightly as possible on the leopold, it's almost impossible to notice because the transition is very smooth. The realforce 55 definitely requires a more conscious push, and you notice when you go over that threshold.
It's not a significant problem, just something that's surprised me a few times since getting my fc660c.