Why was my insert scaled down to the left bottom corner when i put motionblur first and then reformat?

I followed one tut by Mocha: Planar Tracking, VR & VFX Tools. The name is “Webinar: mocha Pro & Nuke workflow”, the second instance —— attach the insert to the back of boy in grey. Webinar: mocha Pro & Nuke workflow - YouTube

Why was my insert scaled down to the left bottom corner when i put motionblur first and then reformat (like tutor said)? But when i put reformat first and then motoinblur, the insert image can be shown properly in the right position. I am so confused. Isn’t it something about the order of motionblur and reformat? I need help.:slight_smile: Thx! (PS: the insert size is 535349, but the project settings has the size of 20481152)

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