Hi there! Thanks for checking it out.
The way my table plays is that it's a 1-to-1, so filling 2 soak instead of taking 2 damage, for example. Usually the players tick the first couple of soaks before having to make decisions to start tagging the HP bar or take a Condition.
A separate playtester told me that their table did it the other way -- that they can check a Soak box to negate all damage for a given hit-- much like triggering an Evade, so there is some precedent in the game. They said it worked really well and led to some tactical choices during the fight scene. However, I would suggest that this means that Soak boxes should not "heal" as rapidly, as they likely represent more significant damage being taken, so maybe switch the way HP and Soak heals if you want this option.
These house rules were written before the Tiny system made those new Heavy Weapon rules. I have not been able to playtest anything, but my gut says that it can be a player's choice-- using Heavy Weapons for a +2 to total damage but also -1 action on your turn, or using Heavy Weapons for +1 to total damage as a normal action. As always, you can never have more than 4 damage in any given outcome.