Certainly, it can be a bit tricky. The biggest problem you will run into is that Cinema's mapping has more freedom than Maxwell's (for instance, by changing R.P or R.B in Texture Tag > Coordinates), so it is easily possible to set up parameters in Cinema which cannot be duplicated in Maxwell. Therefore, if you have to match the two, the way to make sure you can do that is to set it up in Maxwell first (using Fire), and then duplicate that in the Cinema tag, rather than going the other way around.
To set up your example scenario (if I understand it correctly), this appears to be what is needed:
- Scene Object > IBL: Scale U: 1.35, Scale V: 2.65
- Sky Object > Coordinates: S.X: -1 and R.H:-90
- Texture Tag > Coordinates: leave all at defaults
- Texture Tag > Tag: Tiles X: 1.35, Tiles Y: 2.65
At this point things should be matching. Say then that you set Offset U/V to 36° in IBL; convert 36° to 0.1 (36/360), and multiply by the Length X percentage (74.074%) in your Texture Tag, and then make that negative, yielding -7.4%. Doing the same for Offset V, you end up with -3.77% for the Texture Tag's Offset X value. This also should match.