Overlaps in Indian railways

[PJW]

Hi,
        As of my experience I had found three types of overlaps in absolute block working system under colour light signalling for Indian Railways i.e., Signal O/p - 120m, Block O/p - 180m, Intermediate Block O/p - 400m. Can anyone explain me why these are different and how these distances are kept

Unlike in UK a fixed overlap distance of 200yards (183m), why in IR fixed overlap is not followed

Thanks in advance

Don't know about India, but in UK with Absolute Block signalling, the block overlap is 400m, but if the distant is colour light can be reduced to 180m.
The UK does have other overlap lengths- 225m where can be provided particularly on highest speed lines, conversely if speeds are low can justify a reduced overlap less than 180m.