I think you're reading too much into this. As stated the increase in pressure will depend on the case capacity, but there are many other things that have an impact on pressures that the manuals don't even list. Chamber/barrel dimensions, bullet design and construction, general differences is firearms used, differences in atmospheric pressure, temperature, differences in loading tools and techniques, lot to lot variations in components used and etc. What a manual lists as safe may not be safe at all when loaded by someone else if enough of the above meet at a "worst case scenario" circumstance.

Loading manuals are a guide to get you started, they are not a recipe book. Owning a manufacturers manual for every bullet you use is nice for anyone that actually reads the whole book because they will give you information specific to their products, but it isn't needed to work up a good load. The OAL Hornady gives is based on the design of their bullet and has no real bearing on any other brands. The difference in pressure you might get from using another bullet with a different seating depth is only a part of the difference of all the above possilbe factors. The Hornady bullet is swaged which means it is probably softer than the MO castings. Are both bullets in question the same diameter? How do their respective bearing surfaces compare? All of these need to be addressed, not just seating depth, and the best way to do this is simply to start at a reduced or "starting" load and work your way up to a safe load.