2SF2+2SF4 E-DPDCH without ul-DPDCH

The reason why ul-DPDCH is not supported for E-DPDCH with 2SF2+2SF4, is presented in 3GPP TS25.213.

According to Table 0: Maximum number of simultaneously-configured uplink dedicated channels in TS25.213 as below, in case of 4 E-DPDCH channels, there should be no ul-DPDCH configured.

More specifically, you could refer to 3G Evolution: HSPA and LTE for Mobile Broadband. As you can see, when there are 2SF2+2SF4 E-DPDCH configured, there is no extra space for ul-DPDCH in terms of code tree.