Should the antenna ratio values between Magic and openlane agree? I am getting rather signifigant disagreements on what is being flagged

They make somewhat different assumptions (especially around contact layers; information about how contact layers should be calculated into antenna rule checks is lacking and how the calculations ought to be done is pretty ambiguous). Disagreements are supposed to be minor. But there are multiple ways to run antenna checks, all of which are apparently valid under some set of assumptions, and which can produce pretty divergent answers.