Here are some additional sites you can check out that discusses genetics.
www.bettatalk.com
www.bettas-jimsonnier.com
www.bettaterritory.nl
www.bettysplendens.com
They don't really discuss dominant-recessive traits. But as a general guide:
- Traditional or "wild" form is dominant over any modern traits.
- Less rays are dominant over multiple ray branching (eg. VT (less ray) is dominant over HM (multiple ray branching)
- Red is, IMO, partially dominant - I mean they will almost always show, though a mere smudge
- Irid dominant (similar to red)
- females are said to be dominant for form while males more for color (not always true)
Dominant/recessive traits also depends on stronger lines - eg. males from a true line are usually dominant over females from a mixed line. So, IMO, the breeding trend during certain periods will determine probable outcomes.