The open structure area loads in RISA do apply to all members equally, not just to members in that plane. And, the back frame will get the same loading as the front frame... meaning no reduction for shielding.

When we implemented this feature, there was some wording in ASCE-7 that specifically prohibited the consideration of shielding. The rational being that a small angle to the wind load would mean that the back frames get essentially the same load as the front frames.

I'm not sure that this is how engineers who work with trussed towers and such really do their design. But, that's the code provision we were looking at when this was implemented.

For what it's worth, we have a "user request" to change this or to add an option to only consider the current plane. I'll add your name to the list of users who have requested this enhancement.

Thanks Josh. It was my understanding that one either uses the Open Signs/Lattice Framework coefficient and apply it to leeward and windward columns (coefficient is lower and thus smaller pressures), or use the Trussed Tower coefficient (which results in higher pressures) and only apply it to the windward face.

I'm not an expert enough on the wind codes to give you guidance. I'd have to pull open the codes to review them. My experience is with the following:
1) Open structure using much, much older codes (ASCE 7-1995)
2) Building Structures using the current ASCE codes
3) Lattice communication towers design to the TIA-G standard

Based on my experience I would guess that your understanding is correct conceptually. But, ultimately you'll have to pull open the code and review it yourself to make sure that it is correct. If I recall correctly, the SEAoW has a design guides / commentary / manual on the wind code that might be useful to you. Haven't looked through it in years. But, when I did, I found it useful.