I don’t have Max, but from what I recall someone, and perhaps that was @Jarek, figured out that Max’s camera behaves “opposite” of Rhino’s when using an aspect ratio that is not 1.5:1.
Both cameras try to emulate a 35mm camera with their lensing, which has a film gate size of 36mm wide by 24mm tall (which works out to a 1.5:1 aspect ratio). The issue is that in both Rhino and Max you can have viewports that are not 1.5:1, so what does that do to the emulated film gate size? In Rhino, the minimum film gate dimension is always 24mm. What that means is lets say we start with a 1.5:1 aspect viewport, so Rhino is emulating a 36mm x 24mm film gate. as you stretch that viewport wider to say 2:1 aspect, the minimum film gate dimension will be 24mm, that means the gate width will expand to 48mm
In Max as far as I understand, the maximum film gate dimension is 36mm, so as you stretch a a viewport beyond 1.5:1 to 2:1, the gate width will always be 36mm, but the gate height will change to 18mm to get to the 2:1 aspect ratio.
With a 1.5:1 viewport ratio, both Rhino and Max have a 24mm x 36mm gate and should look the same with the same lens. If you stretch the viewport to 2:1, Rhino will have a film gate of 24mm high by 48mm wide, and Max will be 18mm high by 36mm wide. In order to have the same horizontal field of view in this aspect ratio, you would have to multiply the Rhino lens by 1-1/3 (48mm / 36mm), so on a 2:1 aspect viewport, to duplicate a 35mm lens in Max, you would have to use a 46.667mm lens in Rhino.
So the TL;DR, to match lenses, first both Rhino and Max viewport aspect ratios need to match. 1.5:1 is the easiest because at that aspect, lensing will match (in Rhino, viewport size and thus aspect can be set explicitly using -viewportProperties)
To match a Rhino lens to Max, RhinoLensLength = ((24 * [aspect ratio]) / 36) * MaxLensLength
where [aspect ratio] = viewport width / viewport height.