contact fair or foul

[Greyhound]

The ATR says that any otherwise legal tackle that is performed in a careless, reckless or wit excessive force can be penalised.
This is extremely subjective. I tend to call a more clean/less contact game then is popular up here in N. Michigan. I got most my knocks in DC where there was more of a ethnic influence that accentuated skill over strength. Players have to learn to gauge what a reff will allow.
Regarding players of dramatically different heights, I just try to remember that everyone should be given a fair chance to play the ball. Running over the little guuy or gal isnt fair though.
I think what you are describing in the last scenerio is an impeding call with contact. If I felt it was a legal tackle off of the ball I would award an IFK. If it was not legal I would award DFK. IF it was a deliberate foul to stop attacking play it might be a yellow. If it denies an obvious goal scoring opportunity it could be a red.
If I understand you correctly.