I can confirm your proposal ( scalar system of cubits) and the unit you so eloquently express as 20 34/55.
34/55 is a fibonacci relationship and also the bases of Thom's system as 34 and the imperial as 55.
The HFC as 9069/440 can be linked to your unit sequentially as you suggest.
best to use deimals although fractions work better
your unit is A 20.6181818181r
HFC is B 20.61136364
take one from the other
C 0.006818181r the unit of interpretation
A/C = 3024
B/C = 3023
So the relationship is scalar as you suggest. This is my understanding of how the system works but you have given me bucketfuls of information but i feel sure what you suggest will fall within the system and i am not going to check it.
There has to be a reason for the ancient metrology to be the way it is and the fundamental reason was probably the prediction of the eclipse.
Thom's base unit is 816 and multiplied by 55/34 = 1320 ( this is Jim Wakefield) this is another Thom 'proof'
The main idea I am working on is that the system is not man made but was discovered and the best evidence i have seen for this is Jim Wakefield's work involving real Pi.
Thom's work suggests that the numbers are universally sacred ( discovered not invented ) i took this to mean in my first book, so the monuments express this discovery.
The Stonehenge Aubrey circle is the Saxon yard x the megalithic yard x 100 = 897.60 imperial feet. Base 100 is the sacred system as suggested by Thom.