Columbia Viva Tonal and soft tone needles

I have a Viva Tonal 710 (or perhaps 711) and have notived that it sounds very good, but seems a tad quiet with soft tone needles. It sounds great with medium tone needles, quite bold and strong volume. Has anyone else noticed this? what about the larger models? Could it be the soft isolator or is it just the nature of the reporducer? I had it inspected and it does play very nice overall.

I have sealed the horn and such, so that isn't it.