You need a bit of space between the top of the steerer tube and the top of the stem in order to preload the headset bearings. The amount of space varies somewhat to opinion, but 3-6mm is a workable range.

But, you don't want too much space! Too much space could result in excess compression of the stem around the end of the steerer tube as well as less interface.

A general guideline would be to manage your "stack" so that the upper edge of the stem's upper pinch bolt is at or below the top edge of the steerer tube when the stack is under compression. To check yours, you can:

1. Adjust your headset as is. Preload the bearings and tighten the pinch bolts. The headset components are now under compression.
2. Loosen and remove the cap only.
3. View the space between steerer and stem top. View the location of the upper pinch bolt in relation to top edge of steerer.

I'm not there, so can't comment on "safety" of your proposal.