Recently, while experimenting with alternate fingering on different fret positions to minimize big jumps on a specific song, I discovered that on my Ibanez EHB1505, the tonal difference between the B and E string is much greater than my Ibanez SR876. On the SR876, the B is not as thuddy and muffled, and I can play closer to my "home position" at higher frets without it sounding too muddy compared to playing in lower frets at the E string. There's still some difference, but not nearly as drastic as on my EHB1505. On the EHB1505, the difference is so drastic that I can't get it to sound close enough on the B string at the higher fret positions, so I'm forced to have play it on the E string to keep the tone more consistent. The other basses I've had varies in this too (Dingwall, Bongo, NS Design). I'm guessing the culprit is the string gauges. I don't know what gauges are the B and E string on my SR876, since I got it used, so maybe it has a lighter gauge B string that's makes it sound more balanced with the E string? Can I assume that if I got a lighter gauge B string for my EHB1505, I can achieve better balance with the E string's tone?
Most 5 or 6 strings have radically different tone on the B string. 15 years ago the best solution for me was a Sting Ray 5 but it was really heavy.
Do you still have factory default strings (D'Addario EXL165+130) on your 1505? Using a taper wound low-B improves the situation. This is why I chose a 130T for my 1005MS when swapping the default D'Addario EXL170-5SL strings with some NYXL's. Yes, a thinner gauge low-B also gets me clearer notes on higher frets. On my BTB685SC, the factory default were the Elixirs with a 130TW low-B. I've swapped them with quite a few different brands and gauges of strings. One time it even had a 135T D'Addario FlexSteels. Currently, it carries a non taper wound but lighter gauge 120 low-B from Dunlop Super Bright Stainless series. I find the 120 low-B has a good tonal balance with the 100 E next to it when played higher up the frets. Regarding the EHB, one thing you need to consider is that it has a chambered body. Despite electronically, the Big Split pickups on the EHB1505 gets you a brighter tone than the BH2 on the SR876, acoustically, the EHB chambered body will definitely get you a darker tone compared to the SR.