If you park it 'down hill' in the rain, water runs along the gutters and out down the edge of the screen and door pillars. If your dash is not collecting water it COULD be doors seels or even the join in the roof (do you get water in your head liner?) that can run down the inside into the foot wells and you may not notice it.
Have someone spray a hose on and see if you can spot the water coming in (take sandwiches and tea)
This is from my own experience... I have a very slight leak in the join on the roof near the gutter. Once the water starts to come in it is a capillary action and the water flows quickly and steadily into the head lining.
I park mine pointing up hill for now... my foot wells have stayed dry but the back gets wet coz my body cappings are rusted through.
There is a link on this site for the official 'water ingress manual' for the Defender (I kid you not) I have down loaded it...it is what the Dealers use.
Just had a look but cant find it on here... it is 35 pages!...
Can anyone remember posting it or seeing it?
If anyone wants a copy message me with your email and I will send it..... not sure how to post it on here and may be copyright issues?