miller passport

[frankv11]

recently got a miller passport plus, had very little to no time to use it yet. does anybody have any experience with it. I know I just need to get in garage and put in some time. I notice when loading wire I pulled trigger wire speed is slow and then speeds up quite a bit. I assume to get a good start on cold. I'm used to one constant speed especially for short quick welds.
can anybody offer any insight into the reason for change in wire speed and maybe some user tips