Microtonal (24 TET) tuning sounds "wrong"

I have just started using 24-TET (equal tempered quarter-tone) tuning, but the sound I get (albeit musically interesting) is a long way from the tone of the piano being emulated.

My guess (correct me if I'm wrong) is that, because 24-TET tuning uses two octaves on the keyboard to represent one acoustic octave, the pitches of the notes played at the far ends of the keyboard are a long way (around 2.5ˆ±1 times) from the pitches their MIDI codes normally represent, and that, therefore, Pianoteq uses models of strings of inappropriate lengths to generate those notes. The result is that low-mid notes sound like they are played on ridiculously taut bass strings, and the high-mid notes sound like they are played on very slack high strings.

Is there a way to work round this, so that the notes across the keyboard sound more consistent with this kind of microtonal tuning?