In split view, not able to resize windows beyond a limit, the flexibility is very low

So I have Pages on left side & Preview on Right side, I want to resize the pages window to about 1/4 of the screen width but the split view won't allow further resizing after a little distance from the centre.

So the max I can get is 45-55% ratio but I want to resize in 25-75% ratio.

Any Help?

this is the maximum I can drag the slider to the left. (which is tbh still almost in the middle)