This has been asked before and remmber if you have a theory chances are someone has already thought of it and tested it.
In play or for that any rank testing will usually need the use of Excel.
You need to calculate a metric for want you want to test.
You have said broadly "back price decreased the most"
So if a $200 chance decreases to $150 is that what you want or a $3 chance to $2.
What metric % chance or $ value.
Read the manual.
Search the forum.
Formulas like MAX and RANK will be handy (in Excel) as will last_last_traded and remember triggers (in MFP)
Test and fine tune using TM.
You may want to search 'distance' in the forum as well.
Good luck.