Are the rails supposed to sit flush on a USC?

[Srtsam]

I just picked up four aluminum HK rails from hkparts. when i installed them on the rifle, they sit atop of the lug holes. There is no countersink on the underside of rail and as such there is tiny gap on all 4 rails. I kinda like the look but just want to make sure this is correct. The plastic rails I had on it prior sat flush along the top and sides. thanks for the time
sam

[kdcgrohl]

I just picked up four aluminum HK rails from hkparts. when i installed them on the rifle, they sit atop of the lug holes. There is no countersink on the underside of rail and as such there is tiny gap on all 4 rails. I kinda like the look but just want to make sure this is correct. The plastic rails I had on it prior sat flush along the top and sides. thanks for the time
sam

The HK rails have a gap under. HDPS rails do not.
I have the HK rails. If they're good enough for HK they're good enough for me.

[Srtsam]

thank you very much, now i can sleep!!!