Giving you a merit because unlike most posts you at least support your analysis with a few charts. And I mostly am looking at the same thing. Right now however it doesn't look like we will hit the $6400 area yet without retesting the $9100 area resistance within the next few days or weeks.
I agree with this sentiment, a retest of triangle breakdown does seem more likely and the current scenarios that are playing out (Part 2, 4 and arguably 5) include this likelihood.
Descending Triangle Looking Similar To 2018
Interesting comparison, although it employs some curve-fitting.
The chart cuts off the first half of 2018 which makes it look like last year's triangle was
much smaller than it really is. The 2018 triangle was 3x as long (time-wise) than this one, implying a much stronger breakout in percentage terms.
I don't think we can necessarily plan on a 63% decline this time.Agreed, hence the measured move (Part 2) working out to $6,410 instead for the Weekly triangle that broke down, rather than the $5k area of -63% (top to bottom). Consider Part 2 a correction to Part 1 regarding he measured move of the breakdown (hence the title). Part 1 was an extrapolation of the 2017 drop, which I found interesting as it would take the price towards the trajectory of the 200 Week MA for support (where BTC was last supported at it's swing low), but they are not proportionate you are right. The descending triangle also broke down much sooner than that of 2018, as you mentioned, so should not be considered a valid pattern at present.
I don't see how you could extend the triangle any further than the above however. That initial wick down to $6k you see was the first time the price reached this support level.
I'd be happy to see an alternative triangle which shows a drop further than 50%, given the swing high was $12k and the low was $6k, but would consider the evidence if provided.
I'll otherwise try and keep these updated when relevant, if they are still being useful. 
