Why one or two SC-FDMA symbols in UpPTS?

In TDD, SRS can be transmitted in uplink as well as in special subframes (UpPTS).
Based on the special subframe configuration (Table 4.2-1 from 36.211), the UpPTS length varies (one or two OFDM symbols).
When one SC-FDMA symbol exists in UpPTS, it can be used for SRS transmission.
When two SC-FDMA symbols exist in UpPTS, both can be used for SRS transmission and both can be assigned to the same UE.

LTE experts: please tell what it mean 1 sc-fdma and 2 sc-fdma symbols.
As per understanding SRS position is on last symbol of special subframe for TDD. Why it mention 1 or 2 sc-fdma symbols?

They are saying about the no of symbols in UpPTS.
For eg, SSF configuration 0 to 4 is having 1 UpPTS symbol.
SSF 5 to 8 is having 2 UpPTS symbols.