I think it's a little more complex than that. If you look at the temps when we get those cold fronts, you'll note that southern broward gets a little more chill than the rest. The cold air bends in there for whatever reason (see the below screenshot from Florida's Best Fruiting Plants).
My Mauritius is actually located in the front yard, which is the only place that I haven't mulched (lest the HOA and city come after me :-). Also, I know Harry's trees produce exceedingly well on muck, which is basically just really old compost.
I tried an emperor once. It started off as a beautiful tree that produced prodigious crops in a peat based mix and a 15 gal container. As soon as I threw it in the heavy compost of the back yard, it went into steady decline. I suspect that part of the issue was fungus related, but I've also heard of emperors regularly doing poorly in mucky soils.
In my area, the trees that perform regularly are the older ones (generally north of 20 years in ground). South Florida is really a curious and heterogeneous mix of various microclimates. A plant that excels for one person may perform terribly for another person just 2 miles away, and vice versa.
Jeff, I remember reading somewhere that Emperor was recommended for soils with high organic content. The implication was that the high organic soils promoted vegetative growth over blooms in other varieties. I know you have loaded your older yard section full of mulch. Have you planted a lychee in the new section? Maybe you would get increased bloom frequency there with the sandy soil.
My mother, who has more time to care for her trees and her trees are a couple years older had fruit last year and again this year. She lives a mile to the west of me.
