Here's a scope trace of sending three dits at around 25 wpm. Note the shortened length of the first dit and the lower output level compared to the second and third dits.
Here's how three dits look after Winkeyer USB is setup to extend the first dit or dah by 30 milliseconds. While the first dit is now of the proper length, the power level is still lower than that of the second and third dits. The parameter used to lengthen the first code element by the Winkeyer is called "1stExt" for first extension. It works for hand sent code or for messages sent by the PC to the Winkeyer.
Another oddity - there's always a very short noise burst about 25 ms. prior to the start of a dit or dah. Not noticeable on the receiver.
Looking close at the envelope for a dit, the rise and fall times could be a bit longer, but the shapes are pretty good. Here you can see a variation of several percent in the output power level over the duration of the dit.
Floyd - K8AC