De-subticking your jump reduces fall damage due to float precision by mitigating the accumulation of small errors in position tracking when using floating-point numbers. When a character jumps and falls in a video game, their position is continually updated using floating-point values. However, the precision of these values is limited, leading to rounding errors in position calculations. As a result, over long falls, these errors can accumulate, causing the character to be slightly higher in the game world than intended.

By de-subticking the jump, you essentially increase the frequency of position updates during the jump and fall. This means that the character's position is corrected more frequently, reducing the time over which rounding errors can accumulate. As a result, the character's actual position remains closer to the expected position, and the fall damage is reduced because the character falls from a more accurate height, mitigating the impact of float precision issues on gameplay.

Subtick issues in the game can be attributed to the use of PHP in the source code. PHP, being a server-side scripting language primarily designed for web development, may not be the most suitable choice for creating a high-performance game engine. Its execution model and design principles differ from what's typically needed in gaming engines, which can result in subtick problems, such as imprecise physics calculations and game time synchronization.