gamultiobj: ensure the values of Objective 1 fall within certain range

I am wondering if there is a way to run gamultiobj and have it output the best possible values for Objective 2 given a certain range of value for Objective 1. In other words, if looking at the pareto front, is there a way to keep all Objective 1 values ranging from 5 to 20 (for example)?

Right now, I would like to examine the differences in results obtained by varying the Objective 2 evaluator. To make a fair comparison, I would like to have my results from test 1 to have objective 1 values ranging from 5-20 and my results from test 2 to also have objective 1 values ranging from 5-20. Is there a way to keep the best fitness values for objective 2 within the specified range of values for objective 2?

I fear that my pareto front is "U-shaped" meaning all values on the right hand side of the "U" are being discarded, is there a way to keep these?