'DB' has it right. The best you can do is a 'full sized' antenna. The shorter ones can certainly be more convenient, or practical, but they are not as affective. The difference may not be much less, but it's still less affective. Will an inch or two make a lot of difference? Not really, but a foot or two certainly can. Don't get carried away with that 'longer' thingy, there's a limit. That limit for HF is generally a 1/4 wave length. The things advertised as 5/8 wave antennas that are NOT something like 22 feet long are NOT 5/8 wave antennas. They are just advertising 'stuff'. (Works real good as fertilizer but not for much else.)
- 'Doc