The "proper proportions" depend on your definition of "about the size of a cigarette pack"; is it a pack of standard cigarettes? unfiltered? 100's? 120's? 20-pack? 25-pack? 14-pack? half-pack (10)?
My definition is reflected in the image; close to the size of a half-pack of filtered cigarettes. It is compact, ergonomic and closer to the proportions of the magazines of real-world pistols.
A "common cigarette pack"-sized item simply is not viable as a device that fits in the handle of a pistol; the weapon would be practically unusable by human hands, and there is absolutely no way that it could ever fit in the handle of the canon artwork of a laser pistol or sonic sword.
"Depends on the type. Look at the canon artwork for Col Jamison, or the woman in the bubble-head space suit. Is the power pack in the grip, or is it in the "mag well" seen on both weapons?"
Don't you mean Garlus Tylappar, owner/operator of CS Gullwind in Dramune Run? I am not aware of any canon pic of Col. Jameson (Volturnus saga).
Notice that the pistol in the pic in question has the power cable coming out of the bottom of the grip (where the power clip would go), and what you call "the well" has a rounded bottom, indicating that it is likely the housing for machinery/electronics, not a receptacle for a power source.
The girl (who appears with the same weapon in the same module on more than one occasion) has a rifle that, if not for the "bubble" at the end of the barrel would be identifiable as a gyrojet or auto rifle.
A better argument might be had with the laser weapons carried by the Malthar's robots, with power cables (going to power backpacks) coming out of the assembly forward of the trigger.
But there are two fundamental problems with pointing at these as canon for purposes of powerclip sizes:
1) These would be outliers; the 100% canon example of a laser pistol seen all over AD and in early modules simply has no place where it can accommodate a 20-pack of filtered cigarettes.
2) The art is by Clyde Caldwell, who is (or was, I have not seen his work in a while) notoriously bad at weapon design and other equipment (I could literally write a scholarly paper on the subject). Notice the space battle
scene in Dramune Run pp. 28; the three assault scouts have bubble cockpits as if they were fighters, they have the "thrust trails" of three engines (not two), including one from the cargo bays, and are armed with forward-firing beam weapons.
I'd simply suggest giving the Clyde Calwell art the same treatment as is given to the Zeb "equipment diagrams"; accept that they exist, but ignore them otherwise because they violate written canon.
My artwork does not violate canon; it has the proportions of a half-pack of cigarettes and can be seen to be in proportion to canon descriptions and artwork of weapons in the setting. This would not be the case if it were literally the size of a pack of Newports.