See section 18.104.22.168.10 of the rules. Smoke occupies the entirety of a hex like all other terrain, fire and barrages. However, smoke is a hindrance it doesn't block line-of-sight. It's an AP or GP modifier. It also affects calling for indirect fire and movement.
Here is the entry in the upcoming rules index for direct fire smoke:
Smoke, Direct Fire: 5.16.2; 22.214.171.124.10; 126.96.36.199 (Observer Hindered); 188.8.131.52; 184.108.40.206; 220.127.116.11; 6.8.4
The entry in bold, is classified as the primary section in the rules.
Right. I guess my issue is that I couldn't find a phrase that says something along the lines of
When direct firing a smoke round, make an ammo limit roll. If the roll is successful, simply place a smoke counter in the target hex. No other roll is necessary.
This is how I've been playing it. I suppose it should be obvious, but I wanted to double check to make sure I had made the right assumption.
In general the rules are very thorough, but because some topics are broken up into different sections of the rules, sometimes it's hard to find a rule that I vaguely remember reading but want to recheck to clarify. So I'm extremely happy to hear that an index will be included in the upcoming version of the living rules. That should resolve any issue I have with how the rules are organized.
Thanks for the response Jim!