I’ll tell you exactly where it’s coming from. Water goes in the cowl grill and is supposed to drain out a drain hole at the bottom of the front fender just in front of the door. Those holes are either not there too small or plugged up. The water rises in the A pillar and overflows at the “hing pocket”. It then flows onto the rubber threshold and into the footwell instead of running out the door. The threshold is actually slopped toward the inside of the car.
To fix it you need to take the interior vent grill off and the vent door behind it and reach down in the bottom and pull out leaves, dirt, old sandpaper etc. Either the holes are too small or don’t exist. You will need to open them up larger or put the drains in yourself. Just be careful as there is little room for error.
This problem has plagued Avantis from day one and I don’t think they ever realized where the problem was coming from. The fix isn’t hard and is certainly worth the effort.