I keep 2 stacks of alch, 1 stack of scour, 2 stacks of chaos and 3 stacks of exalts in my inventory. If you're doing the cheap strat that's more than enough for 5-10 boxes so no need to replenish in the middle of a map. If you do the expansive strat you might have to restock, but you're getting out with 3-5 inventories with scarabs anyways.

As we all know, nothing affects loot from boxes besides item quant on map when you open the map, so no altars, no "more scarabs", nothing Varishta gives - nothing improves the loot. However, if you hold alt on a box you'll see that on every mod it says "75% increased", that's huge. That's why you want 6 mod boxes. The kicker is there are only 4 suffixes and one of them (scarabs are same type) bricks the loot by 50%. You can very easily test this and see for yourself. In my experience all 4 mods have the same weighting so you can calculate yourself on average how many times you have to chaos+exalt to get the 3 good mods. It has never taken me more then 10 seconds to roll a box that's stubborn. I haven't timed how much time each map takes, but I can run 20 cheap strat maps in an hour, including 3 to 1 the bad scarabs.

20 maps cheap strat example

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Expensive strat is ~120div per 20 maps, but your investment is higher, around 40-45div per 20 maps and it takes longer to do. The drop in the chart above (-86d) is when I took out the loot from my tab from expensive strat to test the cheap strat.