I'm installing a threadless stem on an alloy steer tube. The steer tube was cut too short for the stem, so I need to place a 3mm spacer under the stem. This does not allow me use a spacer between the top of the stem and the cap. Is this an issue? I was told that one should have at least a 5mm spacer between the top of the stem and the cap. Does this rule only apply to carbon steer tubes?

Can I get away with no spacer between the top of the stem and the cap on an alloy steer tube?

I should mention, despite not having a spacer between the top of the stem and the cap, everything seems to tighten up just fine, and feels pretty solid.

Thanks.