Please refer to the Talpatti map posted by @
integra. There is a white line that is touching S. Talpatti. This is an arbitrary line and is not a border demarcation line, because it was not there in 1947 map as S.Talpatti itself was not formed at that time. So, the actual boundary line ends a little NW of S. Talpatti.
Radcliffe Line was drawn basically to demarcate between a small Indian island in the west and a small BD island in the east. It was not meant that the border would keep on moving SE.
But, India started to claim exactly the same. Then came a time when S. Talpatti raised up from the sea sometime after 1947. India thought if it can establish claim on this island then the SE line can be extended further to squeeze BD sea territory.
Now, the S. Talpatti belongs to which country, remains the basic question that must be resolved first. This can be solved by deliberating on, but not limited to, the following points:
1) its location itself, at which side of the contesting countries it is lying? and
2) Soil from which country's river flows are contributing to its formation?
Map shows, it lies on the BD side. Also, Bangladesh has surveyed the flows of rivers and found that the rivers from Bangladesh are carrying soils towards S. Talpatti and are contributing to its formation.
The UN arbitration will certainly take note of many such points. I personally believe BD will get the possession of entire S. Talpatti and as a result the sea border will run south along the west of S. Talpatti.