[r-t] Alliance-ability

[Edmund Mottershead]

I was tinkering with a composition of spliced royal which was coming in too long, and noticed that in each of the leads of Yorkshire the music that I was interested in invariably came before the 1270 in the place notation.
I decided to look for an alliance or little method which began X30X14X50X16X1270, and otherwise fitted into the slot in the composition currently occupied by Yorkshire, and settled on:
X30X14X50X16X1270X38.14.50.16.90-12

However this is just Yorkshire with the last four Xs in the place notation removed.
This property of being 'alliance-able' is shared by Yorkshire Major (June Alliance and X38X14X58X16.12.38.14.78-12), but not Yorkshire Max. It's also not limited to Yorkshire, for example Cambridge Major yields X38X14X1258X36.14.58.16.78-12.

Does anyone on here know if there is there an underlying cause for the property of 'alliance-ability', and hence a way of predicting on which stages of a right-place treble-dodging method it will occur, and in what way, or is it simply a coincidence?

Cheers,
Edmund