You have continuous factors so you might be able to use the *linear factor constraint* to exclude a region instead of a disallowed combination. If I imagine the plot of the design as X1 versus X2, it seems like you want to exclude the upper left corner and the lower right corner. That requirement means that there will be two boundaries that define the excluded corner regions.

Here is an example from our course for the introduction to design of experiments. It involves two continuous factors. In this example, we want to exclude the upper corner, so we use the coordinates of the two corners to define the boundary line and enter this in custom design as a linear combination.

Can you identify such points that could be used to define the two linear combinations for your case?

Learn it once, use it forever!