Some whistles are just plain feeble on these low notes. Generations and Generation clones (Walton, "feadogs", Guinness whistles, Camacs) are particularly bad. Susatos are better and posh aluminium whistles like Albas and Overtons better still. A wider bore goes along with a more powerful low register (but may make the high B a real bugger to play with an acceptable sound quality).

The best overall balance I've come across has been in wooden whistles (one from China and one from Romania, neither of them being the commonly available type from those countries, I just got lucky).

Unfortunately most whistles are sold to people with rock-bottom expectations. At almost *any* price point, the same money spent on a recorder will get you a better designed and better quality-controlled instrument.