should the first course of bricks sit on insulation?

[Gulf]

Yes, it is worth worrying about if it is not too late to fix. It can be all the difference in how well the oven performs IMO.

Edit: You may want to go back and read through a few builds, and download the free DIY brick oven plans from Forno Bravo before you proceed any further.

[microbe]

The topic says it all.

Is the heat lost through transfer from the 1st course to the hearth worth worrying about?