It is generally true that reaction rate is directly proportional to enzyme concentration. However, there are limits to the range of enzyme concentrations over which this is true, due to several possible reasons. (1) As the enzyme concentration increases, the rate may become so fast that the substrate becomes depleted very quickly, and when that happens the reaction slows down. (2) If the enzyme tends to aggregate at higher concentrations into a form with lower catalytic activity, raising the enzyme concentration will not raise the reaction rate as much as it should. (3) If the enzyme stock solution contains something that inhibits the reaction (examples: glycerol, salt, detergent) and a large proportion of the reaction volume consists of the enzyme stock solution, then the reaction rate may not increase in direct proportion to enzyme concentration. (4) The enzymatic reaction rate may increase in a greater-than-linear fashion with increasing enzyme concentration if the enzyme concentration range is comparable to the dissociation constant of the enzyme oligomer into monomers, but only the oligomer is active.

Thanks, Adam. I am new to enzyme work and your answer has helped me understand the possible scenarios that might be occurring. I appreciate your advice.

This guide might help too..

https://www.innovabiosciences.com/blog/enzyme-units-and-specific-activity-explained.html

the linearity do not must be. You must find it experimentally.