Welcome to the forum!
After lots of experimenting with grafting Mangos, I’ve found that high grafts are better than low grafts because the resulting trees tend to grow more vertical and have less tendency to become droopy. Many of my low graft trees, such as those that were epicotyl grafted, tended to grow more horizontal and also tended to flower more precociously and for a significantly longer period of time.
Something to consider with high graft trees is that if there is damage high up on the tree but below the graft line, you will not be able to head back the tree to healthy wood without losing your grafted Variety.
In SoCal, I highly recommend a high graft tree over a tree that was grafted much lower.
Simon