how pseudo direct addressing works?
In MIPS-speak, these areas of memory of 28 (26+2; the +2 is because instructions are four bytes in size) bit address space (256MB) are referred to as "superblocks". Pseudo-direct addressing allows you to jump anywhere within the same superblock. It doesn't matter if it's forwards or backwards.

This was never a problem in practice because it's very rare for a single binary (whether it's an executable or a shared library) to have more than 256MB of code. IIRC, the MIPS linker could handle it if it ever occurred by generating a trampoline. Suppose that the compiler generated a jal, for example, where the linker discovered that the target was in a different superblock. Then the linker would generate a couple of instructions to do the full jump, and point the jal to that.