All the citrus I've seen is grafted low and the scion trained to a single trunk. Commercially in California the tree is allowed to fruit right down to ground level. Most fruit trees in contrast have the lower branches up off the ground. I don't think it matters where the lower branches are, more a matter of preference. There could be some special circumstance somewhere that would make a difference like weed or wildlife issues.

The major problem of leaving a bare trunk is that it can sunburn in some climates and kill the tree. All my Meyer lemons and other miscellaneous citrus are left with branches from the base. Citrus can be pruned as desired; it can even be bonsai. The only real reason to prune citrus is for shape. For some cultural practices it is simpler if the first branches are raised from the orchard floor, as in your foto; if they were my trees I would paint the trunk with white latex paint, the cheapest you can find and diluted 1 to 1 with water; the paint protects the trunk from sunburn; and also retards suckering.

Several of my trees are like yours and some are budded.
My rootstocks are standard trifoliate, trifoliate hybrids,
flying dragon, and sour orange. Rootstock suckering
is more of a problem on the higher cleft grafts.

Be sure to keep any suckers rubbed off, as the rootstock
would rather grow itself than feed the alien grafted scion.

The cleft grafts are advantageous in that they will start
growing and require no special care and will result in more
growth at the end of the year than budded trees. No
fooling around with forcing growth is required.

The higher straight growth is undesirable in climates
where freezes are a problem.

That should not be a problem for you. It does put the fruit that much out of reach.