Hello. As was suggested by a previous poster, the "blocky" feeling was possibly from the checkered walnut grips on the "original" Hi Power you handled.
The Practical is based on the newer Mk III version of the Hi Power but the frame size is the same for the Mk III, Mk II, and the older "classic" Hi Powers.
It differs from current Hi Powers in the following ways:
Most Practicals (but not all) come with a factory ring hammer.
I believe they were offered with either fixed or adj sights. The ones I've shot had the fixed sights.
The frame is hard chromed on the Practical and the gun normally comes with Pachmayr grips where the Mk III comes with the blk checkered nylon and the Standard, the wooden checkered grips mentioned previously.
The front sight on the Practical is normally an unserrated ramp, though later runs did come with the semi-post front sight common to the other Mk III variants.
Essentially, the main difference is the hard chrome on the Practical's frame.
Best.