With 2.5 as a drill there is no back swing; you start at '6/100s' with the club horizontal. When I use it for chipping there is enough of a back swing to get the club to horizontal or slightly higher. My trail elbow starts in front of my hip as described in IMA instruction and there is no attempt to keep it there as the trail arm extends.
I did not make a gif for 4.5 because the Hogan gif said it all. With 4.5 you start with your trail elbow touching your trail hip (slightly forward of the Hogan position if you're IMA) and you maintain that contact while you rotate hips and shoulders from an otherwise normal top of swing position. Ideally you should still have contact at impact and will loose it soon after. If you don't then it's likely you were extending your trail arm vs letting it extend.
More discussion about 4.5 can be found with THIS