define sensitivity requirement

Hi Professionals,

I met a problem for 14.16.1, with pure GSM -108dBm sensitivity and static GPRS -104.5dBm(CS-4) minimum input level(specification is -98dBm for high band) would make
TU high or RA BLER (block error rate) higher than 10% spec.

May some tell me how good should the static GPRS should be that making it strong enough to fading profile input in terms of hardware?

Another question is How comes CS-4 sensitivity has 3~4dB difference from pure GSM? receive IF filter bandwaidth counts?
How can I define well that the problem is non or close to zero Hardware related? What steps should put into trace for the clarification?

Thanks!
Regards,
Wilson