The parameter “Maximum Ratio Threshold of PDCHs in a Cell(%)” defines dyanmic PDCH in a cell. Ratio of PDCHs = Number of available PDCHs/(Number of available TCHFs + Number of available static PDCHs). this parameter under GPRS Attributes/Ps channel management parameters.
NB. For EDGE cell you’ve to look about Abis capacity. Then you will get full performance.