Blue sensitizing dyes do not impart much speed to an emulsion. They just give an intense band at one end or the other of the blue region. If you have such low blue speed, you may be adding too much green or red dyes. After all, sensitizing dyes are desensitizers as well, if used in too high quantity.

That is why most companies use one broad dye for pan sensitization. You might inquire about that at Sands.