Plum progress

So I've started noticing something really interesting about the plum trees this year...but first, a little set up:

I have three 4'x4' raised beds, one right next to the other, running north-to-south.  Each has strawberry plants and a Stark Bros 2-n-1 Japanese plum tree (Shiro and Redheart plums) planted in it.  I put the trees in two years ago, and last spring they bloomed like crazy during an unusually early warm spell, and then temps went back to normal and all the little plums got frosted off.  The beds are really close to each other, so it's not like they're in different micro-climates across the yard, nor are the trees really big, so it's not like each is shading the one to the north.

This year the weather's been a little more consistent, and the trees looked beautiful while in bloom, and we've only had a couple mild frosts since.  What I've noticed however, is that the trees seemed to have ever so slightly staggered blooming (with the southernmost tree blooming just a little earlier, and the southernmost blooming just a little past the middle tree), and they dropped their blooms in the same order.  And now?

Here's a close up of the southernmost tree...see all those little nubbins, often pale on the tip, with no leaf, no bloom and no fruit on it?  Those are spots where the tree DID have blooms and then may have started to form a fruit.  Most of them dropped off.  You can see one tiny plum (probably about half the width of my pinky nail) at the bottom of the picture.

And the northernmost tree?  Loaded with little plums - again, none any bigger than half the size of my pinky nail at this point.  You can also see some little pale plums, and some little empty spurs where a flower or fruit already dropped off.  But the tree is loaded with little fruit!

The little off-colored pale plums are going to drop off.  Many of them I can just barely touch and they instantly detach and drop.  The ones with the dark green plums?  Those guys are holding on firm!

And yes, the middle tree seems to have less than the northernmost tree, and more than the southernmost tree.

So is this just chance?  Or is it that the trees are really every-so-slightly shading the tree to their north, cooling them just a bit, causing them to bloom just a little later, and therefore making them hold out until the temperatures are a bit more ideal?  This is definitely something I'll have to watch in future years!