Also, you might try saving the model and creating a new response to optimize. A good choice would be the root mean square error (RMSE). A column formula could compare the predicted response with the target response using something like this
Sqrt(
Sum(
(P(t1,X) - T(t1))^2 +
(P(t2,X) - T(t2))^2 +
(P(t3,X) - T(t3))^2 +
(P(t4,X) - T(t4))^2 +
(P(t5,X) - T(t5))^2
)
)
where the P(t,X) is the fitted model of the predicted response at time t and excipient level X. T(t) is the target level at time t. You could use the Graph > Profiler with this column to optimize X (minimize response with desirability function).