Yeah, your explanation is crystal clear actually.Not sure how to elaborate, but I will say I thought my Jazz 5 had a slightly thicker inherent tone than my four-string Jazz basses. I'm not surprised that a larger, heavier neck would affect the tone of a bass, which might explain the accounts I've read about L-1505s sounding thicker and/or more balanced than L-1500s.
And I would want thicker tone than my L-1500, which sometimes sounded thin and nasal to me, but this varied enormously across different rigs, and even in different rooms. It usually didn't work so well with my G-K 700RB-II/Neo112 rig, but at one show that combination produced truly monstrous tone. So, at its best, it was unbeatable as a rock stage bass, but I prefer a more predictable plug-and-play experience, so I sold it after I bought an SB-2. All the MFD punch, more consistent heaviness.
For some (stupid) reason I'd assumed a 1500 would roughly sound like a 1505 and left it at that since I'm not currently in need of a four-string. Plus my problem is exactly the opposite of yours: I'd really like a fiver that sounds like the four-string basses I like. I have two fivers, my first bass, one I could never bond with, and the L-1505 which, while sounding real great (not thin and nasal, that I can confirm!) doesn't cover the whole ground I need it to cover and give me options in active mode I don't really need.
Thanks for the extra info!

