Aegisub: Importing Subs Lose Scaling

[Kommandos0]

Whenever I use Aegisub and try to copy and paste styled subs across to another subtitle file the scaling is always off, with the pasted ones usually being smaller then the original. How do I make it so that the scaling stays exactly the same?
For the duplicate version I'm using the exact same subs and video as the original, and no subtitle style settings have changed, they just always seem to never keep the same scale as the original.
Does anyone know how to fix this?

To clarify what I'm attempting to do is copy certain parts from two different subtitle files into one file.

Original:

[Attachment 43270 - Click to enlarge]

Pasted:

[Attachment 43271 - Click to enlarge]

[videobruger]

Is there a (different) PlayResX, PlayResY in the files?

[Kommandos0]

Ah there indeed is. The original is 1440x810 and the new one is 1920x1080.
I'm assuming I just change the new one to the same resolution as the old one?
Is there a way to change the resolution within Aegisub or do I have to do via directly editing the files in notepad?
Sorry I'm very new to this so I'm not 100% sure what I'm doing.

[teodz1984]

Just load the video after loading the ass file...
Aegisub will ask you to scale it with the dimensions of the loaded file..

[Kommandos0]

Thank you that fixed everything!
This will make combining subs so much easier in the future.