Difficulty in understanding the paragraph concerning h- parameters
Suppose you want to characterize the transistor at 1GHz, yet that node has 10pF or 20pF parasitic capacitance what with
1) scope probe
2) biasing circuit
3) mechanical structure to hold the device

At 1GHz, 1pF is -j159 ohms.

At 1Ghz, 20pF is -j 8 ohms.

Thus the realworld prevents "open circuit" tests at high frequency.