I don't claim to be an expert, but here's my guess. Your first method that failed looks like what it's doing is the equivalent of highlighting and selecting 3 cells and then trying to put values in there. The $range->{Value} is expecting a scalar (such as a number or string). So when you try to give it an array, you're giving it something that it's not expecting.

In your second method that is working, your giving $range->{Value} scalars.