Tom,
I know that this is probably a silly response sine you're the commentator and I judge you extremely capable and highly knowledgeable. So, figure that this response is more for the Community at large.
Sometimes when we're irrigating a segmented (stack) wall from below, we'll use butterfly valves (nil psi loss but 100% backflow stoppage). So, you're probably feeding from the top down. With regard to Wizard Lott's response, if you're feeding form the top, you're probably using spot elevations to account for the PSI gain as you go down, but you'll have to subtract the loss for each HCV on the longest furthest run of lateral. The performance data is published. While they can check between 4' and 32', the factory setting is 12' or 7ish PSI. This is a good setting if using 24' radius heads on a 2:1 slope. The loss is roughly .43 PSI per foot of head held. Imagine that. How logical. I round to .5 per foot to be on the safe side and because it's easier to calculate in my head (I'm a simple guy who likes to go to the 10th, not the 100th).
Given the opportunity, I prefer to irrigate stack walls, or long runs of slope from the bottom up. But often, our mainlines are set in the parkway at the top of the slope and we have to feed down. The worst part about this is that in-line check valves are way too often clogged during construction (or soon thereafter) and are not specified to be located in identifiable locations. I've seen wood stakes painted red to identify the buried location. Are you kidding me? Is that wood stake going to be there in 5 years? they can be a maintenance nightmare. We specify them to be located in 10" round valve boxes and identified on the record drawings. That way, WHEN they clog, they can be easier to locate.
Now for a more basic question: If you are going down a 2:1 slope and you are holding 12' (this is just the factory setting but the theory will work for all of the modified settings based on your sub lateral spacing) of water as you are going down the hill and you are placing these HCV's at a 24' distance between your lateral sub feeds since you are using 24' radius heads what is the net loss due to the HCV's? ______ Should be an easy answer if you round to the nearest 10th. Assuming that my calculation is correct (maybe that's a faulty assumption), the HCV's should have no bearing on your critical analysis design calculations. It's a wash.
Good luck with your design. Thanks for the puzzle.