I'm just trying to get my head around where in the rules you are allowed to spend dodge tokens when using Guardian with Obi.

The first line of text from the Guardian ability in the RRG on page 48 states:

While a friendly trooper unit at range 1 and in line of sight is defending against a ranged attack, A unit that has the guardian x keyword may cancel up to x hit results . For each hit result cancelled, the unit with the guardian x keyword rolls a defence die matching its defence.

So the guardian ability cancels the hits, so if the hits are already cancelled, how can Obi then spend 1 or more dodges to then roll less dice that need to be rolled as part of the guardian ability to finish resolving?

I know that it says on Obis card under Soresu mastery that when you spend dodges when defending or using guardian you convert surges to blocks and activate deflect, but mechanically there are no incoming hits to be able to cancel with the dodge tokens as the Guardian ability has already cancelled the hits. Note also that the defence dice you roll as part of the guardian ability are not a defence roll but an effect as part of the guardian ability resolving so you aren't actually in Attack step 7 "Roll Defence Dice" yet.

Also specifically worth noting is that dodges are spent in Attack step 5 "Apply Dodge and Cover" While Guardian does not trigger until Attack step 6 "Modify Attack Dice" Step, so the opportunity to spend dodges even if you in theory could has already passed before Guardian can trigger and be used.

Is this just a case of RAI over RAW for Obi or are there some other rules somewhere I am missing?

Edit:

Ignore me i should have actually read the RRG on Soresu Mastery

I know that you prefer Vaapad, but as a Jedi master you should know Soresu too. At least the theory.