How to understand this memory addressing scheme?

Question

RAM

I don't understand what the shortened address means? The fact that it can be shortened by referring to the register is clear as daylight (such addressing is called indirect through the register). I need to do it without the help of the register. Is that how it's done at all?
The only thing that came to my mind was to increase the word OP. Initially, the OP word is 4 bytes (the amount of information read and written in one write / read operation). If you refer not to 4, but to 8 bytes, then you can shorten the address. Those. apply a shortened address to the address register of the OP, but not count 8 bytes, but count the first 4 or the last 4. Any ideas? Google didn't help.