The right properties to get the 3ds Max Blowup Region working are
SMTDSettings.RegionRenderingMode = #maxRegion --enables the last mode of the Tiles tab's options
SMTDSettings.RegionType = 3 --enables Blowup mode for the 3ds Max region
If you want to use the 3ds Max region definition, just set
SMTDSettings.RegionUseMaxValues = true
If SMTDSettings.RegionUseMaxValues is set to false, you must specify the actual corners, e.g.
In the above example, note that the aspect ratio of the region matches the image aspect of the output. In my case, I had render output set to 800x600, which is of course image aspect 1.3333. If you subtract Left from Right and Top from Bottom, you end up with 521-273=248 and 351-165=186, and 248/186 is 1.3333! The SMTD UI, and 3ds Max’ UI make sure the region aspect is locked. If you set it yourself, it is up to you to ensure that.
Note that the “Blowup” option used to be broken at C++ level in the Lightning.dlx integration plugin in earlier versions of Deadline. It was fixed in Deadline 9 on Feb. 2, 2017.