Full tangs have to have exactly the right contours to get the correct action for when using the kukri. This is a problem the W/S kukri had, along with many MKIII's, also when the slab of horn or wood looses its shape, it can lead to rust on the tang, and because the slabs are no longer flush to the tang, it can make the handle uncomfortable, plus that extra shock of the cut comming back into the hand.
It makes no difference to the shock in the hand felt whether the tang is tapered towards the butt or not (W/S kukri had full length and width tangs), what that does do though is give it a different weight ratio and feel in the hand.
Below is an example of Indian Army Gurkha Issue kukri, butt plate with screws WWI
I hope that is of help, cheers Simon