I'm simulating a single hydraulic fracture using cohesive element in Abaqus, with the same input parameters, I have made 5 models with different value of injection rate in which the first model has the lower injection rate and the last one has the higher injection rate , but I cannot explain the breakdown pressure I got after running these models (see attached picture). I'm expecting that the breakdown pressure will increase with the increase of the injection rate.

Thank you and any suggestion will be helpful to me!