Hey, since 2.0.56 there's a way to modify stack size in container prototype. What do you think about adding this to the loot chest.
https://lua-api.factorio.com/latest/types/InventoryWithCustomStackSizeSpecification.html
Main motivation is that the loot chest can grab stuff from all surfaces but some items are unstackable and even the 120 slots at legendary quality seem like a bottleneck in heavily modded games - even if you have 1 separate chest per surface. Usually most mods avoid large inventory size since that oftentimes causes UPS drops due to the way how the engine handles containers, so raising the stack size instead the slot number seems like a solid solution.
Here's what mine looks like from line 107 in entity.lua
This multiplies all stacks within that particular container prototype x 10'000.
chest.inventory_size = 48
chest.inventory_type = "with_custom_stack_size"
chest.inventory_properties = {stack_size_multiplier = 10000}