Bytes and pixels answer different questions
File size measures how many bytes are stored on disk. Image dimensions measure the pixel grid, such as 1200 by 800. Two files can share the same dimensions while using very different byte counts because format, compression and visual complexity also matter.
Why a small limit can change dimensions
A photo may not fit below a strict byte ceiling even at low encoding quality. Reducing width and height gives the encoder fewer pixels to store. That is why a reliable result should report both the final bytes and the final dimensions.
What increasing KB can and cannot do
Increasing the byte count can satisfy an upload rule. It cannot reconstruct detail that was missing from a low-resolution or heavily compressed source. Use the exact-size tool for compatibility, not as a substitute for a better original image.