Welcome to the Forum!
The "drop" is occurring that happens when boots break-in and quality leather wrinkles at the ankle as riding boots do.
Are your boots to short? Yes.
on the verge of it and going to end up to short in my opinion.
Broken in boots still need to come to the back of the knee joint after they have finished doing the drop and yours are not done with that part of the process yet.
I was much the same when I searched for boots.
I did not want to spend the money for customs, but when you factor in "drop" there is not a boot on the market made that was tall enough to fit my lower leg properly with break-in drop you know is going to occur.
Add in small ankles and larger muscled calf and anything off the the shelf did not fit, period.
If I remember correctly, when my measurements were done either 2.5 - 3" extra height was made into the pattern to allow for the wrinkle drop the boots were
going to develop because when your ankle drops when astride the leather shall follow. So yes, your boots are to short.
When my customs were new they bothered me to wear, not to ride in but to wear prior to riding because they were so tall the leather tops were cutting the back of my knee every step...after a few wearings and the beginning of the break-in started, the leather top softened then slid to the correct height and I can do anything at anytime in my boots they are so comfortable now.
My boots are pull-on, no zipper or gussets in them and truly a custom fit comfortable.
I would suggest if you not have them get full boot trees along with the foot piece so the foot not curl and the boot shaft stays as upright supported as possible not bending at the ankle as so many unsupported ones do.
Today custom boots are a lot of money, but so are off-the-shelf ones that are quality leather made and unless you fall into that small percentage of perfect leg dimensions, they don't fit great, tolerated but not great.
I will never regret spending the money for customs, but it was a chunk of change to commit...and so worth it.
I offer you good luck in what you are going to do...