Music Theory

I'm not sure if everyone else has as much trouble understanding chord progressions as I do but I find most explanations a little vague.
I liked the description in chord wizard in as much as I understood it, It was explained as the varying of tension to pull the listener along.
Looking closer I feel a progression is close to a melody as in the undulating nature caused by the rise and fall of notes. Close intervals between notes giving a gentle move and larger intervals giving a  harsher move.
I can understand that to a degree; as long as dealing with root movement but chord progressions involve movement from or to inverted chords. This is why i struggled to understand chord movement with inverted chords.
I feel i have understood the subject a little better and even more so by trying to explain it in this post which i leave for anyone who would care to comment.
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Table one is an arrangement of the relative chords arranged to show < (descending) and > (ascending) INTERVALS from central chord "I".
If unclear please refer to previous post.

Table one
m7                           M2
m7  m6                      M2 M3
m7 m6  Tri                 M2  M3 Tri
M7 M6 P5   P4            m2 m3  P4  P5
m7  M6 P5  P4   m3       M2 m3 P4  P5  M6
m7 m6  P5  P4  m3  m2  M2 M3 P4  P5  M6  M7
ii   iii   IV   V   vi   vii   "I"    ii   iii   IV   V   vi   vii
------Descending----<   >------Ascending------

Table two an alternative arrangement of the relative chords useful for calculating progressions involving inverted chords.

Table two
vii   V   iii   I   vi   IV   ii

Table two has two simple rules.

Rule 1
Any first inversion chord can  be considered to be just above root position of chord on left.
Example In key of C vii(bdf) in first inversion=dfb which is just above root position of chord on left which is ii(dfa).

Rule 2
Any 2nd inversion chord can be considered to be just below root position of chord on right.
Example In key of C ii(dfa) in second inversion=adf which is just below root position of chord on right which is vii(bdf).

Note from vii next chord LEFT=ii and from ii next chord RIGHT=vii

Note as with most things in music there are different perspectives so rules 1 & 2 could be.
Any root position chord could be replaced by the chord on LEFT in 2nd inversion or,
Any root position chord could be replaced by the chord on the RIGHT in 1st inversion
Most of the time these substitutions would mean exchanging a Maj chord for a min chord or visa versa.

Calculating a chord progression when both chords are in root position is simply a case of deciding.
1 what your moving from
2 what your moving to ie a 2nd, 3rd,4th etc
3 which direction up a 2nd as in ii to iii or down  a 2nd as in iii to ii etc
Moving from root chord built on V note of current key DOWN to root chord built on I note of current key is a move of a descending Perfect 5th.
Moving from root chord built on V note of current key UP to root chord built on I note of current key is a move of an ascending Perfect 4th.

Calculating a chord progression when either one or both chords are inverted is easier if the inverted chord is temporarily replaced with nearest root chord.

1 Establish the current chord and inversion and temporarily replace with root chord
2 Decide the degree of movement ie 2nd, 3rd, 4th etc from the current chord.
3 Decide the direction of movement
< descending ie below current chord
> ascending ie above current chord

Example 1 in key of C major, V in 1st inversion up a 2nd

1 V in 1st(BDG) can temporarily be considered to be vii(bdf)
2 The move a 2nd
3 The direction > above current chord

V(1st)_temp vii up to  I(root)=m2> or BDG up to CEG=a min 2nd ascending

(Note V(1st)_temp vii down to I(root)=<M7 or BDG down to CEG=a Maj 7th descending)

Example 2 in key of C major, V in 2nd inversion down a 2nd

1 V in 2nd(DGB) can temporarily be considered to be iii(EGB)
2 The move a 2nd
3 The direction < below current chord

V(2nd)_temp iii down to ii(root)=<M2, DGB down to dfa=a Maj 2nd descending

(Note V(2nd)_temp iii up to ii(root)=m7>, DGB up to dfa=a min 7th ascending