Finally got my HiSenior B5+ and got to listen to it for a few days.
1) holy hell, these are super tip/fit dependent. On stock, they sound neutralish from bass to Mids w/ a muted treble. After trying all my available tips, they sound the best for me w/ tips that are a bit smaller than my regular fit(M), and have wide bore
2) They sound relatively balance. Quick mid bass, sub bass extension is good but is a bit lean in rumble and power. Mids are my favorite, clear and positioned well. Doesn't lack body or is it thick, very nice vocals, both male and female. Very good treble sparkle and extension without a hint of sibilance and peaks.
For 100usd, these are a steal.
i recently settle for the Final Audio E tips or the KZ starline tips. for me i like using small bore with the B5+. like you, sometimes i would use the one size down tips to give it a more airy and thinner mids sound, but it all depends on the songs.
now that i think of it, how tip dependent the B5+ is ultimately became it's strength to me. i can bring only one iem and several different sets of tips to alter it's sound as i please (i use the B5+ with bluetooth cable as this is my daily driver)