tatra805 wrote:

done some thinking about this earlier also

Even with the airtop under the back seats it takes a while to get temps up in the low area's.

probably as hot air moves upwards

Another way to look at this is that there is no need to direct hot air to the back, it is sufficient to circulate the cold air and mix it with the hot air to evenly warm up the whole interior.(although this will slow down the process)
So some hidden ventilators sucking in from passenger foot area and disposing it in the front footwell works just fine.

This is a natural process happening anyway (but very slowly so inefficient) if you turn on the heater/ventilaton you will feel cold air dropping in the front footwell from under the front seats (no its not the non sealed battery box venting as this is also noticeable when stationary).

Recirculation the cabin air works quicker as you suck in from passenger footwell but things get condensed quickly in wet

weather.

2cents