Originally Posted by
79pmooney
Will the bottom pulley swing forward another inch? If so, I'd say you dialed this in perfectly. Looks isn't the issue. You want the chain long enough to allow for a hiccup on the freewheel/cassette and not tear up the derailleur. (That torn up derailleur leads to all sorts of other bad consequences.) But a chain longer than that leads to sloppier shifting on the smaller cogs. Now, if this derailleur is at its limit for swing forward, add links!
If to your eyes, this doesn't look right, well good. A reminder this is a gear you do not want to be in.
If I understand correctly, that's the position on the 42, NOT the 45? If so, and you know not to try that same cog with the 45, I say go for it. To paraphrase Detective Callahan, " a drivetrain's got to know its limitations".
You know what you've set up, just be cautious.