Tapering the bag is nice, as long as it is a straight taper.

The spi will get wet, either becouse you drop it in the sea, it rains, spray, capsizes/cartwheels or you scoop water into the snuffer. You can cut small holes in the bottom part of the bag to let rainwater, seawater in the spi etc. drain if the bag is positioned so flat that it dont drain out the end. Or you can get/make a bag from a material (swimming pool cover?) which lets water trough while offering low friction. We have used a ripstop nylon (not sailcloth) bag succesfully for some years now, but ripped it during the swedish nationals. Will be making a new one in mylar with small draining holes along the bottom.