Cross Posting this:
There are some real amateur-hour mistakes that shipped with many of the forge pieces.
Aside from the old poorly matched non-grid-standard size differences as there where in Reach with a lot of pieces, there are misplaced/mis-aligned pivot points , which are sometimes aligned/placed at a completely illogical point (not even the usual point, at the centroid, as it was in Reach and 3, which I maintain was a bad choice for modular assets) and magnets (that are placed on edge centers, again instead of the potentially more logical corner for ideal modular piece alignment).
There are also improperly unwrapped/sized lightmap UVs, some even appear to have overlapping UVs, so if one small part of your object is in shadow, a whole 'nother portion of the piece will have the same lighting, even if it is supposed to be lit the polar opposite way. This would explain why some pieces change lighting drastically when you come near them (Because they are Lerp'ing from the low-res/improperly-unwrapped baked shadow to real-time shadows). Some good examples of this are the entire set of Ravine unique forge pieces, especially the side bases. If this is the case, and it seams to be, it can in some ways be worked around, but I have yet to find the perfect solution.
The instant radiosity they have is also kind of disappointing in terms of completely enclosed interior maps without windows; as it only does one pass.
Any more passes would be prohibitively expensive and time-consuming. Although, it seems like they could have easily adjust a value or two under the hood and have it spend a little longer generating the lighting and in the process render out more shadow maps, which would contribute more samples making their radiosity far smoother.
They have the lightmap resolution for it in most places, and it would just take a bit more time to get the higher quality result. (e.g. 2x longer light generation time = 2x smoother gradients for indirect lighting and so on, linearly, if Im not mistaken)
Their single pass radiosity only subtracts lighting, and their method has a very short reach. It does not add any ambient light through diffuse interreflectance, or recursivly bounced light, so this is where you get the effect where there is no ambient lighting to give you depth cues and the walls and the floors are indistinguishable similar to that example that I posted screenshots of, back when they showed off that forge map on impact.
So, moving on to
Some tips for forgers:
If you have an interior or enclosed map, add some transparent windows, holes in the ceilings/walls, or open-topped high ceilings.
Most importantly, do this even if this doesn't shine any direct/bright sunlight onto your playable sections, since this will still contribute (in a potentially splotchy, low-res and ugly way if done carelessly) to the map's indirect lighting and add some depth and directionality cues.
This should help mitigate the inevitable eye-cancer that we will all develop when forge maps start to make their way into MM as they did in Reach.
It may help to actually block just the direct sunlight hitting parts of your map by using far-off floating coliseum wall pieces. Because the ambient lighting works subtractively,
if your map has good visibility of the sky/surroundings and some complex geometry, this will allow you to play with indirect lighting which can contribute a lot of interesting color.
I can post examples after I play around with it some more, so far I am still brainstorming ideas.
In addition, the color of your indirect lighting somewhat obviously is controlled by the immediate/directly-visible surroundings. So if your pieces are directly over the oceans on Ravine, the under-sides will receive the blueish green indirect light, and if their over the forerunner parts they will receive grey blue indirect lights and so on and so forth. What's funny is that this even works with things that should definitely not contribute indirect light, like completly shadowed/surrounded patches of grass. This means you might have to place forge pieces outside/bellow your map just to block indirect light coming from illogical sources.
Definitely put some time into deciding on the location of your map, don't just put it all over the ocean way outside of the bounds of ravine like most people do when they start, but experiment with putting half of it over the grassy sections and half over the ocean for the best possible indirect lighting color-range. Remember that to get indirect light your piece needs to be shadowed from the sun, but also at least partially exposed to the sky or other bright surroundings, so don't go making completely enclosed, underground flood type maps that end up with completely flat, grey-brown ambient lighting like I keep seeing on YouTube.