UPDATE: Bad news - any mods automatically disables achievements. But I prefer to play with this mod and get Zero achievements.
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"The player's hit-box is roughly twice the width of what you'd expect from an FPS game..." (c) Civvie11

Ok, this is the "hard" topic about gameplay balance, because on one hand you're having problems with dodging projectiles, but on another hand you can't go through the gaps leading to the late sections of the level (as is intended by developers).

Still, almost every player complained about this game design choice, so here goes the opposite decision - the player can dodge projectiles like in any similar FPS game, but your level routing is up to your conscience.

So I've created a very simple mod which just changes the player's radius (width).

I'm aware of a complex rebalance mod made by someone, who implemented the different option - chaging every projectile parameter to make a similar effect. This sounds resonable, but "width reduction" is enough because it's impossible to finish the game with Good Ending if you'll speedrun the levels. Plus, you still can't go through some puzzle colums (they are still blocking you). But in any case, even with my mod you have to check every corner of every level if you want a Good Ending. But at the same time you'll save more nerves about fighting monsters.

DOWNLOAD:

www.moddb .com/games/powerslave-exhumed/addons/player-hitbox-fix-by-dexiaz

Alternate link:
www.mediafire .com/file/hlk4ik4n3py9l2e/Hitbox+fix+by+Dexiaz.7z

UPDATE:
I've made an alternate hitbox patch, it also changes the "step height" parameter to make climbing out of water easier.
www.mediafire .com/file/t30gyszpr02enyd/hitboxalt.rar

Just extract the "mods" folder to your PowerSlave Exhumed game folder. This automatically enables the mod, so you can just run the game!

(Alternatively, you can write a command line parameter for the game in Steam, it will be like:

 -file mods/hitbox.kpf

 It's not neccesary for you, but I'll keep this to solve potential problems).

I hope it will help you to get a better game experience!