Hello, Bill.
I have to agree with you. There is always confusion created when it comes to forward motion or grabbing a stack of chips and betting less.
The simple solution is to declare your bet, or push the intended bet forward and return your hand to a rest position.
I remember a player from long ago. He would pick up two stacks of chips, one in each hand, move forward and drop a single chip! It was very unnerving, especially when you were about to bet and from the corner of your eye, you could see him picking up his stacks ready to pounce!

It might have been "within the rules" but it was highly unethical.
There were times when he would pick up his chips and the opposing player, or players, would actually surrender their hands before he even bet! His antics often times would stop a player in front of him from betting because he convinced them he was going to call or possibly even raise.
This is why I've always been in favor of a betting line. You cross the line, you've made a bet...no questioning if the chips were pushed out far enough...and, oh yes, if you pick up a stack and move forward across that line, you are committed to that amount.