I agree, although I used your guide and made DTM for a Vial and had some false positives on a Woodwitch Icon also on that bank tab, must be based on pure
chance that this happened and they both have black points in the exact same pixels.
I just don't use the boundaries of the object for all my DTMs, I much prefer grabbing the main color in the area but that is just me. So I just make Tol = 15 for all
points and still get pretty precise finding although instead of 1 x, I get 10-12 x's but overlapping eachother, this gives some randomness to my clicking I believe,
could be a type of in-script antiban in a sence.
Look at runes in your inventory, sometimes the left side of the rune is completely flat for some reason. The boundary method would not find the left
boundary because it switched from round to flat and then the DTM would not be found. To each their own =) I just believe picking daughter points inside the
boundary is not bad idea at all.
I was using white boundaries for my DTM walking and other player points would mess it up and the boundaries of walls move around depending on angle so
I moved on to using assorted colors for the DTM, working good so far.
Look at the water rune missing a side ^.^

or these non-round runes
or squared on 2 sides runes?

Not sure if this only applies to runes but the shape changes when interacted with, I also noticed pouches would go corrupted once place into inventory,
may be they are messing with the item boundaries to throw us off.
Using your guide, I just made this DTM:

This is the matches it gave me:

May be I am doing it wrong but that is what happens when I use outlines with 255 Tol on mother point.
This is what I do for 15 Tol:

This is the result:

No false positives, randomization in coordinates but doesn't lose accuracy due to size of the object. What do you think?