Tom,
The weight of the oven dome and floor are at least 4" inside the outer edge of the enclosure (the space of the insulation and enclosure walls), so the oven will basically rest on the part of the hearth that sits directly on the block stand. Which is good.
I think the round base is cool -- and you will see many of them in the FB Forum. Also, take a look at FB Photos -- where there are hundreds of oven photos.
Brick Pizza Oven Photos | Pizza Oven Photos | Pizza Photos
Hope this makes sense.
Where were you in Italy? We were in Florence for three years, and would still be there -- except that our older daughter was ready for high school. Oh well; I guess she had to grow up, and we're happy with the new school. :-)
James